by

William R. Veal
The University of North Carolina-Chapel Hill
CB #3500
Chapel Hill, NC 27599-3500

and

James G. MaKinster
Indiana University
School of Education
201 N. Rose Ave.
Bloomington, IN 47405

Pedagogical content knowledge (PCK) has been embraced by many of the recent educational reform documents as a way of describing the knowledge possessed by expert teachers. These reform documents have also served as guides for educators to develop models of science teacher development. However, few of the current models accurately address the role of PCK in science teacher professional development. This paper presents two taxonomies that offer a relatively comprehensive categorization scheme for future studies of PCK development in teacher education. The General Taxonomy of PCK addresses the distinctions within and between the knowledge bases of various disciplines, science subjects and science topics. The Taxonomy of PCK Attributes identifies the various components of PCK and characterizes their relative importance based on previously published studies. These organizational frameworks will serve to organize and integrate future research efforts.

Science teachers have been recently introduced to documents that represent the collective thinking of many national leaders in science education. These documents detail what and how science should be taught in schools. The two most notable documents are the Benchmarks for Scientific Literacy developed by the American Association for the Advancement for Science (AAS, 1993) and the National Science Education Standards (NSES) developed by the National Research Council (NRC, 1996). These publications were developed to guide the reform effort in science curriculum development and teacher practice. The NSES states, "The current reform effort requires a substantive change in how science is taught; an equally substantive change is needed in professional practices" (p. 56). In order to implement such a change in professional practice, the NRC recommends the creation of national professional development standards. Since their publication, these professional development standards have been used as criteria for science education reform (National Science Teachers Association [NSTA], 1999).

One important aspect of these education reform documents is the "call" to change science teacher education. The NSES states, "Implicit in this reform is an equally substantive change in professional development practices at all levels. Much current professional development involves traditional lectures to convey science content and emphasis on technical training about teaching" (p. 56). Similarly, Cochran, King, and DeRuiter (1991) stated that the professional preparation of science teachers was often separated or disjointed. Hewson and Hewson (1988) emphasized that this separation occurred when prospective teachers learned pedagogy apart from subject matter. Some science education reform efforts have recently begun to bridge the gap between the pedagogical and content aspects of science teacher preparation by advocating the development of a cohesive knowledge base (Doster, Jackson, & Smith, 1994). Pedagogical content knowledge (PCK) has been suggested as one knowledge base for science teacher preparation (Anderson & Mitchener, 1994). Anderson and Mitchener (1994) have suggested that PCK could be an alternative perspective from which science educators could view secondary science teacher preparation. The epistemological concept of PCK offers the potential for linking the traditionally separated knowledge bases of content and pedagogy.

Historically, knowledge bases of teacher education have focused on the content knowledge of the teacher (Shulman, 1986). More recently, teacher education has shifted its focus primarily to pedagogy, often at the expense of content knowledge (Ball & McDiarmid, 1990). Research on pedagogy has focused on the application of general pedagogical practices in the classroom, isolated from any relevant subject matter. However, several researchers (e.g., Ball & McDiarmid, 1990; Magnusson, Krajcik, & Borko, in press) have rekindled the discussion about the importance of teachers’ content knowledge in learning to teach.

Shulman (1986) developed a new framework for teacher education by introducing the concept of pedagogical content knowledge. Rather than viewing teacher education from the perspective of content or pedagogy, Shulman believed that teacher education programs should combine these two knowledge bases to more effectively prepare teachers. The use of PCK as a topic for research and discussion about the nature of an appropriate knowledge base for developing future science teachers has steadily increased since its inception (NRC, 1996; NSTA, 1999; Tobias, 1999).

The topic of developing future teachers also extends beyond science teachers and "traditional" teachers. Darling-Hammond (1991) cited several studies demonstrating that teachers admitted to the teaching profession through alternative programs (e.g., emergency licensure, private schools, and out of content assignments) had difficulty with pedagogical content knowledge and curriculum development. The current reform initiatives in science provide a guide for some teacher educators to develop models of science teacher development (Bell & Gilbert, 1996; Cochran, DeRuiter, & King, 1993; Cochran, King, & DeRuiter, 1993; Magnusson, Krajcik, & Borko, in press; Sakofs et al., 1995). Some of these models have been specific to PCK development of pre-service science teachers (Cochran, DeRuiter, & King, 1993; Cochran, King, & DeRuiter, 1991; Magnusson, Krajcik, & Borko, in press). Recently, the National Science Teachers Association (NSTA, 1999) developed science teacher preparation standards that highlight the need for teachers to develop PCK. These standards are intended for use in accreditation reviews of science teacher preparation programs for the National Council for Accreditation of Teacher Education (NCATE, 1994). Accordingly, teacher educators continue to recognize the need for an adequate model for teacher preparation.

Currently, there are few models for secondary teacher development (Bell & Gilbert, 1996; Cheung, 1990; Sakofs, et al., 1995; Saunders, et al., 1994). As part of the standards for accreditation, the National Council for Accreditation of Teacher Education (NCATE, 1994) demands that professional education programs adopt a model that explicates the purposes, processes, outcomes, and evaluation of the program. The taxonomies in this paper warrant construction and analysis for two reasons. First, there exists a "traditional" polarization of content and pedagogy in science preparation programs. Second, current models fail to accurately address and outline the role of PCK in science teacher professional development. Professional development in this paper will refer to secondary science teacher preparation. The current NSTA, NCATE, and NSES documents support the idea of models for teacher development. In particular, science reform initiatives on the national and state level are beginning to require more rigorous standards for certification. As part of the certification process, developmental models are needed to guide science educators through the labyrinth of knowledge bases. This paper presents two taxonomies that can serve as models for secondary science teacher preparation.

Pedagogical content knowledge was first proposed by Shulman (1986) and developed with colleagues in the Knowledge Growth in Teaching project as a broader perspective model for understanding teaching and learning (e.g., Shulman & Grossman, 1988). This project studied how novice teachers acquired new understandings of their content, and how these new understandings influenced their teaching. These researchers described pedagogical content knowledge as the knowledge formed by the synthesis of three knowledge bases: subject matter knowledge, pedagogical knowledge, and knowledge of context. Pedagogical content knowledge was unique to teachers and separated, for example, a science teacher from a scientist. Along the same lines, Cochran, King, and DeRuiter (1991) differentiated between a teacher and a content specialist in the following manner:

Pedagogical content knowledge has also been viewed as a set of special attributes that helped someone transfer the knowledge of content to others (Geddis, 1993). It included the "most useful forms of representation of these ideas, the most powerful analogies, illustrations, examples, explanations, and demonstrations-in a word, the ways of representing and formulating the subject that make it comprehensible to others" (Shulman, 1987, p. 9).

Furthermore, Shulman (1987) stated that PCK included those special attributes a teacher possessed that helped him/her guide a student to understand content in a manner that was personally meaningful. Shulman wrote that PCK included "an understanding of how particular topics, problems, or issues are organized, presented, and adapted to the diverse interests and abilities of learners, and presented for instruction" (1987, p. 8). Shulman also suggested that pedagogical content knowledge was the best knowledge base of teaching:

Some research that has stemmed from the introduction of PCK has attempted to address the question of how pre-service teachers learn to teach subjects that they already know or are in the process of acquiring (Grossman, 1990; Grossman, Wilson, & Shulman, 1989; Gudmundsdottir, 1987; Magnusson, Borko, & Krajcik, 1994; Marks, 1991).

Classification is the taxonomic science in which a system of categories or attributes is established in a logical structure (Travers, 1980). Taxonomies have been used to define such diverse entities as plants, animals, fungi, algorithmic processes, and educational objectives. For example, taxonomies in science have included those developed by Aristotle, Linnaeus, and Lavoisier. These and others have been used to classify animals and plant species based upon observable characteristics (Cronquist, 1979; Honey & Paxman, 1986; Raven, et al., 1971). Taxonomies have also been developed in other science domains to aid people in learning about processes and models. For example, in chemistry taxonomies have been used to distinguish between the difficulty levels of Lewis Structures (Fujita, 1990), and to organize organic reactions (Brady, et al., 1990). Taxonomies have been developed and implemented in a variety of areas within science education (e. g., Chin & Brewer, 1998). They have served to assist in the evaluation of educational objectives (Scott, 1972; Stigliano, 1984; Travers, 1980); critical thinking skills (Gilbert, 1992; Pavelich, 1982); course goals (Allen & Wolmut, 1972); state, district, and school curricula (Brown, et al., 1989; Eaves & McLaughlin, 1981; North Carolina Department of Education, 1985); conceptual change (Dykstra, 1992); and biology misconceptions (Fisher & Lipson, 1982).

In the broadest sense, a taxonomy defined in the field of education is a ‘classification system’ (Woolfolk, 1993). Taxonomies in education have focused mainly on evaluation and objectives (Bloom, Engelhart, Furst, Hill, & Krathwohl, 1956). Krathwohl et al. (1964) described a taxonomy in the context of educational objectives as:

The single most pervasive taxonomy in education is Bloom’s taxonomy (Bloom, et al., 1956). It was intended to help ‘teachers, administrators, professional specialists, and research workers’ discuss and deal with ‘curricular and evaluation problems’ (p. 1). Early reviewers of this taxonomy identified five principle uses for its hierarchical structure (Moore, 1982). In addition, Hill (1984) noted four salient features of Bloom’s taxonomy that could be applied to other taxonomies: 1) existence of classes; 2) hierarchical classes ordered in terms of complexity; 3) cumulative nature; and 4) generality in the processes of the various classes. The objectivity of the parts, the ability to organize behavior into categories and the pyramiding structure of the hierarchy made Bloom’s cognitive domain taxonomy relevant to many different fields of education. Therefore, it has greatly facilitated the development of educational curricula and evaluation devices. Bloom, et al. (1956) wanted to create "a theoretical framework which could be used to facilitate communication among examiners." The committee members felt that a taxonomy was an economical way to facilitate meaningful dialogue in their professional field of education. Over a period of time, the education community accepted Bloom’s taxonomy because the taxonomy had appropriate symbols, precise and usable definitions, and consensus from the group that used it.

Only two explicit taxonomies are present in the science education literature (McCormick & Yager, 1989; Neale & Smith, 1989). Neale and Smith (1989) constructed a configurations checklist, or taxonomy, for evaluating teaching performance. The features of this checklist included: lesson segments, content, teacher role, student role, activities/materials, and management. The checklist pertained to conceptual change teaching in science. A teaching performance was rated for each feature of the checklist in terms of high vs. low implementation.

McCormick and Yager’s (1989) taxonomy of teaching and learning science incorporated five categories or domains of science education. The taxonomy was designed to help students become scientifically and technologically literate. The five hierarchical domains were organized by importance: (a) Knowing and understanding (scientific information), (b) exploring and discovering (scientific processes), (c) imagining and creating (creative), (d) feeling and valuing (attitudinal), and (e) using and applying (application and connections). The taxonomy listed what students could do or learn in each domain. McCormick and Yager (1989) contended that too often, science education limited students to the first two domains that primarily focused on the processes and products of science. They stated that the other three domains needed to be included more often in science instruction due to the increased focus on science, technology, and societal issues.

Previous discussions and models of PCK in science education have not been classified as taxonomies (Cochran, King, & DeRuiter, 1991; Magnusson, Krajcik, & Borko, in press; Morine-Dershimer & Kent, in press; Shulman & Grossman 1988; Smith & Neale, 1989; Tamir, 1987). Many of these researchers listed attributes or components of PCK, but did not illustrate their hierarchical relationships. However, these lists of attributes are similar to taxonomies because of the relationships and connections among the attributes (Tamir, 1998, personal communication). These relationships suggest useful ideas for teaching, and they have resulted in an endless number of professional discussions.

Typically the attributes of these PCK models are represented so that the overlap or relatedness of all the attributes determines the amount or development of PCK. Smith and Neale (1989) described PCK as having three components: knowledge of typical student errors, knowledge of particular teaching strategies, and knowledge of content elaboration. They stated that "many of these kinds of teaching knowledge would be in simultaneous use during science teaching and that their integration would contribute to the complexity of teaching" (Smith & Neale, 1989, p. 4). Smith and Neale believed that the integration of the components was vital to effective science teaching.

Along similar lines, Cochran, King, and DeRuiter (1991) defined PCK as "the manner in which teachers relate their pedagogical knowledge to their subject matter knowledge in the school context, for the teaching of specific students" (p. 1). This definition incorporated four components: knowledge of subject matter, knowledge of students, knowledge of environmental contexts, and knowledge of pedagogy. They used two Venn diagrams to show how the four components overlapped, and how PCK was centralized within the overlaps. The first diagram represented the integration of the four components in a novice teacher. The second larger diagram represented the integration of the four components of an experienced teacher symbolizing the ‘extra knowledge’ gained from years of experience. Another difference in the two Venn diagrams was the amount of overlap between the four components. The Venn diagram for the experienced teacher showed greater overlap, symbolizing increased integration of the four components, thus greater PCK development.

Magnusson, Krajcik, and Borko (in press) conceptualized PCK for science teaching as consisting of five components. "Orientations toward science teaching" consisted of the beliefs about the purposes and goals for teaching science at different grade levels. The beliefs were the basis of a ‘conceptual map’ that guided the instructional decisions of the teacher. "Science curriculum knowledge" consisted of knowing about the goals and objectives of curricula (state, national, and vertical) and knowing about specific curricular programs. "Knowledge of the students’ understanding of specific science topics" involved knowing the requirements of learning and the areas of student difficulty. "Assessment" involved knowing specific instruments, procedures, approaches, and activities for a specific unit. "Instructional strategies" included knowing subject-specific strategies, topic-specific strategies, and situation-specific PCK.

The similarities between these PCK taxonomies can contribute to an understanding of which attributes might be considered to be most important. The three most predominant and recurring characteristics in these taxonomies were knowledge of the students, knowledge of content, and knowledge of instructional strategies (pedagogy). These taxonomies have taxonomic characteristics described by Krathwohl et al. (1964). They are based upon previously published literature and are supported by the methods and arguments herein. The purpose of this paper is to describe two pedagogical content knowledge taxonomies and discuss their implications for science education.

The steps used to develop the PCK taxonomies in this paper paralleled the steps used by Bloom et al. (1964). The development of the General Taxonomy of PCK is based on an expansion of previously published PCK categories. Just as Bloom’s taxonomy was designed to order behavior phenomena, the General Taxonomy of PCK was designed to order levels of specificity. Bloom and colleagues presented the steps used to develop their taxonomy: (a) Gather a large list of educational objectives from their own institutions and the literature, (b) determine which aspect of the objective stated the behavior intended and which part stated the content or object of the behavior, (c) find divisions or groups into which the behaviors could be placed, (d) divide the objectives into subdivisions from the simplest behavior to the most complex, (e) define the subdivisions so that group members could communicate. The same steps were modified to produce the PCK taxonomies in this paper.

To produce the General Taxonomy of PCK we gathered a large list of educational, science educational, chemical, and physical terms from the research literature and high school textbooks. Second, we determined which terms were associated with content, pedagogy, and pedagogical content knowledge. Third, we clearly defined the terms, so that they could be placed into logical divisions or groups. Finally, we organized a general scheme that placed the groups into a hierarchical arrangement from the broadest conceptions of pedagogical content knowledge (general pedagogical content knowledge) to the most specific (topic specific pedagogical content knowledge). This taxonomy attempts to represent a typical hierarchical process by which prospective secondary science teachers obtain different knowledge bases contributing to their PCK development.

The development of the Taxonomy of PCK Attributes was based upon the various attributes and characteristics of PCK presented in the science education literature (Shulman, 1986, 1987; Hashweh, 1987; Tamir, 1987; Shulman & Grossman, 1988; Smith & Neal, 1989; Ball & McDiarmid, 1990; Darling-Hammond, 1991; Cochran, King & DeRuiter, 1991, Cochran, DeRuiter, & King, 1993; Magnusson, Krajcik & Borko, in press). A list of all previously described PCK attributes was generated. From this list we were able to determine the most prevalent attributes, as well as generate a rather complete list of the epistemological components contributing to the development of PCK. These attributes were then used to design a taxonomy that represents the nature and relationships of the knowledge bases contributing to the development of PCK. The order and placement of these attributes within our model was based on previously published articles. The taxonomy was evaluated using the criteria outlined by Bloom et al. (1956) and Krathwohl et al. (1964) and compared against examples of existing taxonomies in science and education.

Theoretical views from the literature were used to formulate the developmental structure, content, and processes within these taxonomies. The General Taxonomy of PCK classifies different types of pedagogical content knowledge previously mentioned in the literature and presents an additional category of PCK that will provide a broader foundation for future research. The Taxonomy of PCK Attributes clearly illustrates the inter-relatedness of PCK attributes and their hierarchical relationships (Cochran, King, & DeRuiter 1991; Magnusson, Krajcik, & Borko, in press; Morine-Dershimer & Kent, in press; Shulman & Grossman 1988; Smith and Neale 1989; Tamir 1987). The categorization and sequencing of epistemological attributes related to PCK development is inherently problematic. Yet, these taxonomies will provide a foundation for future research and ways of organizing science teacher development.

The General Taxonomy of PCK developed in this study was organized hierarchically (Figure 1). The foundation of this taxonomy describes general teaching skills or pedagogy that should be developed by all teachers. These pedagogical strategies include, for example: planning, teaching methods, evaluation, group work, questioning, wait time, feedback, individual instruction, lecture, demonstration, and reinforcement. These strategies are not related to any specific content area, and can be used across content areas. Pedagogy becomes a component of PCK only when it is specified within the parameters of educational content areas.

General PCK. The first level within this taxonomy is general PCK. It is implied that an experienced or expert teacher with general PCK would have a sound understanding of pedagogical concepts. General PCK is more specific than pedagogy, because the concepts and strategies employed are specific to the disciplines of science, art, history, math, or English. General PCK is the same as what Magnusson, Krajcik, and Borko (in press) called subject-specific PCK strategies, where subject meant the content area of science. However, restructuring and renaming this category will serve to clarify the use of PCK in educational research.

Magnusson, Krajcik, and Borko (in press) described nine orientations or subject-specific PCK strategies for teaching science: process, academic rigor, didactic, conceptual change, activity-driven, discovery, inquiry, project-based science, and guided inquiry. These orientations represented "a general way of viewing or conceptualizing science teaching" (p. 5). Magnusson, Krajcik, and Borko (in press) felt that these orientations were subject-specific, because their

goals and purposes focused on science. For example, the learning cycle is a subject-specific orientation, because it can be applied to specific science concepts and processes. In the current model (Figure 1), the learning cycle is considered a general PCK strategy for science.

General PCK orientations might be applied to other disciplines, but the processes, purpose, and content or subject-matter would not be the same. For example, art teachers use the critical analysis approach to teach landscapes. The critical analysis approach is very similar to what science teachers call guided inquiry and discovery. First, the art teacher introduces known artists, pictures, and stories about landscape art. Second, students have to analyze the differences and similarities of different landscape paintings through discovery, discussion, and research. Finally, the teacher uses a hands-on approach to have students paint landscapes with watercolors. The teaching strategies in science and art are similar, but they are discipline specific.

Magnusson, Krajcik, and Borko (in press) might say that just because the student is involved in the process of painting, does not mean that the student has the same purpose for the activity as a chemistry student does when determining an unknown in the laboratory. In science, determining an unknown also involves the processes of discovery and guided-inquiry, but focuses on a chemistry compound rather than a painting. In addition, scientific inquiry encompasses the processes of predicting, testing, hypothesizing, logical thinking, and proposing alternative explanations, which are higher order process skills taught in secondary science (NRC, 1996). This unique combination of attributes present in science-specific guided inquiry exemplifies how pedagogy can be discipline-specific and is best viewed in the context of general PCK. Even though the process skills of predicting, testing, and hypothesizing can be learned and developed in other disciplines, these skills become unique and intended when applied to science concepts.

Domain-specific PCK. Domain-specific PCK is more distinct than general PCK, because it focuses one of the different domains or subject matters within a particular discipline. For example, if chemistry was the subject matter, then an understanding of how to teach it to students would be characteristic of a teacher having developed domain-specific PCK. Domain-specific PCK is positioned between disciplines and domains of science to represent a different level and specificity of subject-matter and pedagogy (Figure 1). For example, a performance based laboratory in chemistry might use chemicals and titration pipettes, whereas a performance based laboratory in biology might involve dissecting a shark. Both activities involve the laboratory within the disciplines of science, but the individual tools and purpose are specific to the subject matter or domain. Magnusson, Krajcik, and Borko (in press) referred to this type of PCK as topic-specific.

Topic-specific PCK. The most specific and novel level of the general taxonomy is topic specific PCK. Theoretically, a teacher who has knowledge in this level of PCK could have a solid repertoire of skills and abilities in the previous three levels. Each domain or subject of science has its own list of concepts, terms, and topics, some of which overlap (e.g., Magnusson & Krajcik, 1993). Although the concepts unique to each domain may be taught differently, the common concepts are also taught differently on many occasions. For example, thermodynamics is a common concept found in physics and chemistry, yet this topic is typically introduced differently in the different domains. The corresponding laboratories and demonstrations are different, as well as the relevant examples used in each textbook. In chemistry, a laboratory to exemplify heat content that can be found in various chemistry textbooks and laboratory books is the burning of a peanut. The same laboratory is almost never found in physics textbooks or laboratory manuals. In another example, when discussing heat and temperature, a chemist might use the kinetic molecular theory to describe temperature. Whereas the physicist might say that temperature is just the measure of heat lost or gained in a system. Even though each concept being explored is found in both domains, the teaching styles, methods, and approaches to representing these topics usually differ. These differences legitimate the need for developing topic-specific PCK as an instructional paradigm for prospective science teachers.

Kuhn’s (1962) ideas outline the inherent distinction present among the different domains of science. The chemist develops way of thinking, and uses it to perceive and describe new or different phenomena. For example, if a chemistry teacher were to see a laboratory that introduces the concept of conservation of energy, then he/she would view the laboratory as a possible introduction to exo- and endothermic reactions. This is different than the view of a physicist. He/she might perceive the conservation of energy as a law applicable to electricity or heat within a system. Using this type of argument, Kuhn illustrated the difference among the world views within different fields of science.

A similar argument can be used to support topic-specific PCK. Kuhn (1962) provided the example of an investigator who hoped to learn something about how scientists understood the atomic theory. The investigator asked a distinguished physicist and an eminent chemist whether a single atom of helium was or was not a molecule. Both answered without hesitation, but their answers were quite different. For the chemist, the atom of helium was a molecule because it behaved like one with respect to the kinetic theory of gases. On the other hand, the physicist stated that the helium atom was not a molecule because it displayed no molecular spectrum. Presumably both men were talking of the same particle, but they were viewing it through their own research training and practice. Paradigm differences of this sort can be influential in science, education, and science education. These differences embody the distinctions provided by topic-specific PCK. Physics and chemistry teachers develop the same divergent world views as physicists and chemists. Just as scientists prepare for a career in a particular field, such as chemistry and physics, so must a chemistry teacher and a physics teacher prepare for membership into their respected communities. The taxonomy of PCK types presented in this paper reflects this distinction between physics and chemistry teachers and the common topics they teach.

Many researchers have described and defined pedagogical content knowledge incorporating different attributes or characteristics (e.g., Cochran, King, and DeRuiter, 1991; Magnusson, Krajcik, & Borko, in press). The various descriptive accounts and definitions in the literature have placed little significance on the "development" of pedagogical content knowledge. The only diagram that included an example of the development of pedagogical content knowledge was created by Cochran, King, and DeRuiter (1991). The Taxonomy of PCK Attributes in Figure 2 possesses several unique characteristics compared to previous models. It details a hierarchical structure for pedagogical content knowledge and its attributes. The central location of pedagogical content knowledge signifies its importance. The surrounding attributes are all connected, representing an integrated nature of the epistemological components.

The hierarchical structure suggests that a strong content background is essential to the development of pedagogical content knowledge. Content knowledge can be general, domain-specific or topic-specific. The second most important attribute a science teacher needs in developing PCK is a strong and thorough knowledge of their students. Only after a teacher understands or realizes the importance of the student component of teaching, can the other attributes of pedagogical content knowledge be learned or developed. The Taxonomy of PCK Attributes does not imply a linear progression of knowledge development. Rather, the taxonomy represents a multifaceted and synergistic developmental relationship between the various attributes. However, this does not preclude the significant impact of other social forces (e.g., teaching the way we were taught, teaching to the test, and efficiency of transmission).

One of the most significant aspects of the Taxonomy of PCK Attributes (Figure 2) is the placement of pedagogical knowledge. Pedagogical knowledge is not as important in this taxonomy as it has been in other PCK models (Morine-Dershimer & Kent, in press; Shulman, 1987; Tamir, 1987). In this treatise, the knowledge of the students component has more significance compared to pedagogical knowledge. A knowledge of the students includes understanding possible student errors and misconceptions. Figure 2b portrays content knowledge and knowledge of students as embedded in one another because student errors and misconceptions are more easily recognized when a teacher knows the content topics and concepts. Finally, only after a teacher develops a solid understanding of his/her students can he/she apply any of the other eight attributes appropriate to the student, domain, or concept. This does not imply that a prospective teacher does not already possess some of the other eight attributes. Rather, prospective teachers develop and integrate the eight attributes into a coherent manner more readily when content knowledge and knowledge of students have been developed.

The eight embedded attributes of PCK are not arranged in a hierarchical manner because they can be developed and understood by the teacher at any time during their teaching career. The attributes are inter-related; thus, the development of one can simultaneously trigger the development of others. For example, pedagogical knowledge and assessment are usually learned in methods classes. The knowledge of when, how, and why assessment is used combines two attributes. To extend this argument, when a prospective teacher experiments with performance assessment, he/she will probably integrate his/her knowledge of instructional methods to make sure the assessment device is fair (Payne, 1992). The attributes used in this taxonomy can also be found in expert and experienced science teacher literature (Tobin & Fraser, 1990; Tobin & Garrett, 1988).

The integration of all ten attributes can occur in stages, cooperatively, or separately. For example, a teacher might decide to introduce the concept of crystal structure (content knowledge) using rock specimens from local geologic formations (knowledge of context). The teacher can then employ performance based assessment (knowledge of students’ learning styles) by asking students to match rocks to crystal lattice structure models. Either attribute could have been developed separately; however, the development of PCK requires one to integrate different types of knowledge. In addition, the variety of ways that a teacher can develop one or many of the PCK attributes also implies that there is no one prescriptive way to impart PCK to a teacher.

The interconnectedness of the Taxonomy of PCK Attributes promotes the idea of a teacher as a life long learner. Pedagogical content knowledge is a construct along a continuum. Individuals possess varying degrees of PCK, but they continually develop each of the attributes throughout their teaching career. It might be possible to develop all attributes in a science methods and curriculum class, but the usefulness, impact, and understanding will not be fully realized or integrated until a teacher has acquired several years of classroom experience (Clermont, Borko, and Krajcik, 1990; Tuan, Jeng, Whang, & Kaou, 1995). The pyramid model does not imply that becoming an effective teacher is a linear process. Rather, it implies that a prospective secondary science teacher develops their content knowledge and learns about student differences while integrating other attributes. Usually, content knowledge is developed before knowledge of students for secondary science teachers. Over time, a teacher’s "pyramid of knowledge" grows in size due to a combination of teaching, professional development, and informal learning experiences.

The development of these pedagogical content knowledge taxonomies warrants an operational definition of pedagogical content knowledge. Pedagogical content knowledge is the ability to translate subject matter to a diverse group of students using multiple strategies and methods of instruction and assessment while understanding the contextual, cultural, and social limitations within the learning environment. The term translate is used instead of transform (Shulman, 1987), because content is adjusted to fit a teacher’s understanding of the students. For example, just as Spanish words are translated into English, science concepts are translated into understandable units of meaning for students. When a person translates a phrase or idea from one language to another, the translator must know; the audience’s level of understanding, the correct words to use, the order in which to place words, the cultural context, hand gestures, and social innuendoes. When the principles of translation are applied to science, the teacher must have the associated knowledge of a translator (knowledge of students, content, pedagogy, context, and environment) to properly convey his/her message (chemistry or physics) and/or provide appropriate opportunities for students to discover various science concepts and content within an activity or laboratory.

The General PCK Taxonomy and the Taxonomy of PCK Attributes provide a relatively comprehensive categorization scheme for future studies of PCK development in teacher education. The continued interest in PCK as an epistemological category and as a knowledge base for science teacher preparation has produced a need for a conceptual framework upon which future PCK studies can be based. The taxonomies in this paper provide such a framework. First, the General Taxonomy of PCK will allow researchers and teacher education programs to more accurately identify and address distinctions among knowledge bases of various educational disciplines, science subjects, and science topics. In other words, it will provide a classification scheme for implementing unique instructional methods in the science classroom. Second, the Taxonomy of PCK Attributes will enable researchers studying knowledge development in teachers and teacher education programs to identify and characterize different attributes of science teaching. In addition, this taxonomy recognizes the relative importance that researchers and educators have given to the different components of PCK. These types of organizational frameworks will serve to organize and integrate research efforts centered around PCK.

The use of these taxonomies as a foundation for future research will also provide a model for science teacher preparation. For example, secondary science education programs could focus on developing topic-specific PCK in prospective teachers. Many prospective science teachers know their content well, but they have not learned how to transform or translate that knowledge into meaningful units for instruction. By focusing on topic-specific examples, laboratories, and demonstrations, prospective secondary teachers can focus and develop specific strategies. What is necessary is the effective use of exemplary models of science teaching within topics that can later be transferred to another topic or domain. They can then apply these strategies to other topics and domains based upon their content backgrounds.

Directly or indirectly, teacher education programs will benefit from further PCK research. One obvious area of future research would be to focus on identifying and classifying the various types of PCK employed in the science classroom. This would allow both teachers and teacher educators to more easily identify PCK development in themselves and their students. The ability to track PCK development will enable science teacher preparation programs to modify their classes and curricula appropriately. It is our hope that these taxonomies will provide a foundation for future research and further discussion concerning the preparation of science teachers.

Finally, the identification and classification of the various types of PCK does not exclude the consideration of science areas that combine one or more of the traditional disciplines (i.e. biochemistry, physical ecology, geophysics, etc...). Once researchers are able to identify various components of PCK in the traditional scientific disciplines, then they can begin to examine how teachers contend with these "new" areas of science. Disciplines such as biotechnology are rapidly becoming an integrated portion of the new science curriculum (AAAS, 1993; NRC, 1996). It is vital that we, as educators, develop an understanding about how to teach these new subjects in a manner that reflects the knowledge of today’s science in contrast the traditional discipline-bound courses (Hurd, 1997).

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About the authors...

William R. Veal is an Assistant Professor of Science Education, at The University of North Carolina-Chapel Hill, CB #3500 Chapel Hill, NC 27599-3500

James G. MaKinster is a doctoral student in the Department of Curriculum and Instruction at Indiana University, School of Education 3130, 201 N. Rose Ave., Bloomington, IN 47405. Email: jmakinst@indiana.edu.

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