Research in the area of educational technology has often been critiqued for a lack of theoretical grounding. In this article we propose a conceptual framework for educational technology by building on Shulman's formulation of ''pedagogical content knowledge'' and extend it to the phenomenon of teachers integrating technology into their pedagogy. This framework is the result of 5 years of work on a program of research focused on teacher professional development and faculty development in higher education. It attempts to capture some of the essential qualities of teacher knowledge required for technology integration in teaching, while addressing the complex, multifaceted, and situated nature of this knowledge. We argue, briefly, that thoughtful pedagogical uses of technology require the development of a complex, situated form of knowledge that we call Technological Pedagogical Content Knowledge (TPCK). In doing so, we posit the complex roles of, and interplay among, three main components of learning environments: content, pedagogy, and technology. We argue that this model has much to offer to discussions of technology integration at multiple levels: theoretical, pedagogical, and methodological. In this article, we describe the theory behind our framework, provide examples of our teaching approach based upon the framework, and illustrate the methodological contributions that have resulted from this work. The important thing in science is not so much to obtain new facts as to discover new ways of thinking about them. -Sir William Henry Bragg The advent of digital technology has dramatically changed routines and practices in most arenas of human work. Advocates of technology in education often envisage similar dramatic changes in the process of teaching Education, 2000; Zhao, 2003) . It has become clear, however, that our primary focus should be on studying how the technology is used (Carr, Jonassen, Litzinger, & Marra, 1998; Mishra & Koehler, 2003) . Some of this oversight can be attributed to the lack of theoretical grounding for developing or understanding this process of integration (American Association for the Advancement of Science, 1999Science, , 2001 Issroff & Scanlon, 2002; Selfe, 1990) . Most educational technology research consists of case studies, examples of best practices, or implementations of new pedagogical tools. Of course, good case studies, detailed examples of best practices, and the design of new tools for learning are important for building understanding. But they are just the first steps toward the development of unified theoretical and conceptual frameworks that would allow us to develop and identify themes and constructs that would apply across diverse cases and examples of practice. As Selfe argued, [An] atheoretical perspective . . . not only constrains our current educational uses of computers, but also seriously limits our vision of what might be accomplished with computer technology in a broader social, cultural, or educational context. Until we examine the impact of computer technology . . . from a theoretical perspective, we will continue, myopically and unsystematically, to define the isolated pieces of the puzzle in our separate classrooms and discrete research studies. Until we share some theoretical vision of this topic, we will never glimpse the larger picture that could give our everyday classroom efforts direction and meaning. (p. 119) Developing theory for educational technology is difficult because it requires a detailed understanding of complex relationships that are contextually bound. Moreover, it is difficult to study cause and effect when teachers, classrooms, politics, and curriculum goals vary from case to case. One approach, called design experiments, honors this complexity and has recently gained prominence in educational research (Brown, 1992; Cobb, Confrey, diSessa, Lehrer, & Schauble, 2003; Design-Based Research 1018 Teachers College Record Collective, 2003. Design experiments, as a research methodology, emphasize the detailed implementation and study of interventions with evolving pedagogical goals in rich authentic settings. It acknowledges the complexities of classroom teaching and enlightens both practitioners and researchers by leading to the development of theoretical ideas grounded in contexts of practice; design experiments narrow the gap between research and practice, between theory and application. Over the past 5 years, we have been involved in conducting a design experiment aimed at helping us understand teachers' development toward rich uses of technology while simultaneously helping teachers-both K-12 teachers and university faculty-develop their teaching with technology. This work has informed theory and practice and has been represented through a range of publications. Our work has been aimed at theoreticians and researchers, as well as practitioners and educators. We have published this work in the name of theory (Ferdig, Mishra, & Zhao, 2004; Mishra, Koehler, & Zhao, in press; Mishra, Zhao, & Tan, 1999) In this article we step back from the individually published pieces to offer a bird's-eye view of the conceptual framework that has emerged from this body of work. This is precisely one of the main goals of conducting design experiments: to not only use theory to provide a rationale for the intervention or to interpret findings but also to help ''develop a class of theories about both the process of learning and the means that are designed to support learning' ' (Cobb et al., 2003) . Having a framework goes beyond merely identifying problems with current approaches; it offers new ways of looking at and perceiving phenomena and offers information on which to base sound, pragmatic decision making. In this particular context, the implications of developing a framework go beyond a coherent way of thinking about technology integration. We argue that a conceptually based theoretical framework about the relationship between technology and teaching can transform the conceptualization and the practice of teacher education, teacher training, and teachers' professional development. It can also have a significant impact on the kinds of research questions that we explore. In the sections that follow, we will address these related issues in the following order: (1) We introduce the technological pedagogical content knowledge (TPCK) framework for thinking about teacher knowledge and how it informs the debate on what teachers need to know (and how they might develop it); (2) we show how our pedagogical approach to teachers' Technological Pedagogical Content Knowledge 1019 professional development, learning technology by design, leads to the development of TPCK; and (3) we discuss, and provide examples of, how this framework has guided our research and analysis of the effectiveness of our pedagogical approach. An additional goal of this article is to offer an example of a research program that brings together the pragmatic and the theoretical, the practical and the abstract. We hope to show that the power of this multifaceted program lies in the combining of these different approaches and in its ability to speak to researchers and practitioners alike. The basis of our framework is the understanding that teaching is a highly complex activity that draws on many kinds of knowledge. Teaching is a complex cognitive skill occurring in an ill-structured, dynamic environment (Leinhardt & Greeno, 1986; Spiro, Coulson, Feltovich, & Anderson, 1988; Spiro, Feltovich, Jacobson, & Coulson, 1991) . Like expertise in other complex domains, including medical diagnosis (Lesgold, Feltovich, Glaser, & Wang, 1981; Pople, 1982) , chess (Chase & Simon, 1973; Wilkins, 1980) , and writing (Hayes & Flower, 1980; Hillocks, 1986) , expertise in teaching is dependent on flexible access to highly organized systems of knowledge (Glaser, 1984; Putnam & Borko, 2000; Shulman, 1986 Shulman, , 1987 . There are clearly many knowledge systems that are fundamental to teaching, including knowledge of student thinking and learning, and knowledge of subject matter. Historically, knowledge bases of teacher education have focused on the content knowledge of the teacher (Shulman, 1986; Veal & MaKinster, 1999) . More recently, teacher education has shifted its focus primarily to pedagogy, emphasizing general pedagogical classroom practices independent of subject matter and often at the expense of content knowledge (Ball & McDiarmid, 1990) . We can represent this bifurcated way of looking at teacher knowledge as two circles independent of each other (Figure 1 ). For 1020 Teachers College Record instance, different approaches toward teacher education have emphasized one or the other domain of knowledge, focusing on knowledge of content (C) or knowledge of pedagogy (P). Shulman (1986) advanced thinking about teacher knowledge by introducing the idea of pedagogical content knowledge (PCK). He claimed that the emphases on teachers' subject knowledge and pedagogy were being treated as mutually exclusive domains in research concerned with these domains (Shulman, 1987) . The practical consequence of such exclusion was production of teacher education programs in which a focus on either subject matter or pedagogy dominated. To address this dichotomy, he proposed considering the necessary relationship between the two by introducing the notion of PCK. PCK exists at the intersection of content and pedagogy. Thus, it goes beyond a simple consideration of content and pedagogy in isolation from one another. PCK represents the blending of content and pedagogy into an understanding of how particular aspects of subject matter are organized, adapted, and represented for instruction. Shulman (1986) argued that having knowledge of subject matter and general pedagogical strategies, though necessary, was not sufficient for capturing the knowledge of good teachers. To characterize the complex ways in which teachers think about how particular content should be taught, he argued for ''pedagogical content knowledge'' as the content knowledge that deals with the teaching process, including ''the ways of representing and formulating the subject that make it comprehensible to others'' (p. 9). For teachers to be successful, they would have to confront both issues (content and pedagogy) simultaneously by embodying ''the aspects of content most germane to its teachability'' (p. 9). At the heart of PCK is the manner in which subject matter is transformed for teaching. This occurs when the teacher interprets the subject matter and finds different ways to represent it and make it accessible to learners. The notion of PCK has been extended and critiqued by scholars after Shulman (for instance, see Cochran, King, & DeRuiter, 1993; van Driel, Verloop, & De Vos, 1998). In fact, Shulman's (1986) initial description of teacher knowledge included many more categories, such as curriculum knowledge and knowledge of educational contexts. Matters are further complicated by the fact that Shulman has himself proposed multiple lists, in different publications, that lack, in his own words, ''great cross-article consistency'' (p. 8). Our emphasis on PCK is based on Shulman's acknowledgement that pedagogical content knowledge is of special interest because it identifies the distinctive bodies of knowledge for teaching. It represents the blending of content and pedagogy into an understanding of how particular topics, problems, or issues are organized, represented, and Technological Pedagogical Content Knowledge 1021 adapted to the diverse interests and abilities of learners, and presented for instruction. (p. 8) Our emphasis on PCK is consistent with the work of many other scholars and recent educational reform documents. Since its introduction in 1987, PCK has become a widely useful and used notion. For instance, in the area of science education, scholars such as Anderson and Mitchner (1994) ; Hewson and Hewson (1988); Cochran, King, and DeRuiter (1993) ; and professional organizations such as the National Science Teachers Association (NSTA, 1999) and National Council for the Accreditation of Teacher Education (NCATE, 1997) have all emphasized the value of PCK for teacher preparation and teacher professional development. An analysis of Teacher Educator's Handbook (Murray, 1996) shows Shulman as the fourth most cited author of the close to 1,500 authors in the book's author index, with an overwhelming majority of those references made to this concept of PCK (Segall, 2004) . The notion of PCK since its introduction in 1987 has permeated the scholarship that deals with teacher education and the subject matter of education (see, for example, Ball, 1996; Cochran, King, & DeRuiter, 1993; Grossman, 1990; Ma, 1999; Shulman, 1987; Wilson, Shulman, & Richert, 1987) . It is valued as an epistemological concept that usefully blends the traditionally separated knowledge bases of content and pedagogy. We can represent Shulman's contribution to the scholarship of teacher knowledge diagrammatically by connecting the two circles of Figure 1 so that their intersection represents PCK as the interplay between pedagogy and content (see Figure 2) . In Shulman's (1986) words, this intersection contains within it ''the most regularly taught topics in one's subject area, the most useful forms of representation of those ideas, the most powerful analogies, illustrations, examples, explanations, and demonstrations-in a 1022 Teachers College Record word, the ways of representing and formulating the subject that make it comprehensible to others'' (p. 9). Although Shulman did not discuss technology and its relationship to pedagogy and content, we do not believe that these issues were considered unimportant. When Shulman first made his argument, issues surrounding technologies weren't foregrounded to the extent that they are today. Traditional classrooms use a variety of technologies, from textbooks to overhead projectors, from typewriters in English language classrooms to charts of the periodic table on the walls of laboratories. However, until recently, most technologies used in classrooms had been rendered ''transparent'' (Bruce & Hogan, 1998) , or in other words, they had become commonplace and were not even regarded as technologies. In contrast, the more common usage of technology refers to digital computers and computer software, artifacts and mechanisms that are new and not yet a part of the mainstream. Thus, though Shulman's approach still holds true, what has changed since the 1980s is that technologies have come to the forefront of educational discourse primarily because of the availability of a range of new, primarily digital, technologies and requirements for learning how to apply them to teaching. These new technologies incorporate hardware and software such as computers, educational games, and the Internet and the myriad applications supported by it. These new technologies have changed the nature of the classroom or have the potential to do so. Consider the aspects or examples that Shulman provided as being important to PCK, such as ''the most powerful analogies, illustrations, examples, explanations and demonstrations,'' or, in other words, ''the ways of representing and formulating subject'' to make it more accessible and comprehensible. Clearly, technologies play a critical role in each of these aspects. Ranging from drawings on a blackboard or interactive multimedia simulations to etchings on a clay tablet or Web-based hypertexts to the pump metaphor of the heart or the computer metaphor of the brain, technologies have constrained and afforded a range of representations, analogies, examples, explanations, and demonstrations that can help make subject matter more accessible to the learner. Though not all teachers have embraced these new technologies for a range of reasons-including a fear of change and lack of time and support-the fact that these technologies are here to stay cannot be doubted. Moreover, the rapid rate of evolution of these new digital technologies prevents them from becoming ''transparent'' any time soon. Teachers will have to do more than simply learn to use currently available tools; they also will have to learn new techniques and skills as current technologies become obsolete. This is a very different context from earlier conceptualizations of teacher knowledge, in which technologies were standardized and relatively stable. The use of technology for pedagogy of specific subject matter could Technological Pedagogical Content Knowledge 1023 be expected to remain relatively static over time. Thus, teachers could focus on the variables related to content and pedagogy and be assured that technological contexts would not change too dramatically over their career as a teacher. This new context has foregrounded technology in ways that could not have been imagined a few years ago. Thus, knowledge of technology becomes an important aspect of overall teacher knowledge. What is interesting is that current discussions of the role of technology knowledge seem to share many of the same problems that Shulman identified back in the 1980s. For instance, prior to Shulman's seminal work on PCK, knowledge of content and knowledge of pedagogy were considered separate and independent from each other. Similarly, today, knowledge of technology is often considered to be separate from knowledge of pedagogy and content. This approach can be represented as three circles, two of which (content and pedagogy) overlap as described by Shulman, and one circle (technology) stands isolated from these two. Figure 3 represents the knowledge structures that underlie much of the current discourse on educational technology. That is, technology is viewed as constituting a separate set of knowledge and skills that has to be learned, and the relationship between these skills and the tried and true basis of teaching (content and pedagogy) is nonexistent or considered to be 1024 Teachers College Record relatively trivial to acquire and implement. The design and implementation of workshops or teacher training programs that promote the learning of specific hardware and software skills as being sufficient to round out teachers' knowledge bases for teaching with technology are direct consequences of this perspective. However, the relationships between content (the actual subject matter that is to be learned and taught), pedagogy (the process and practice or methods of teaching and learning), and technology (both commonplace, like chalkboards, and advanced, such as digital computers) are complex and nuanced. Technologies often come with their own imperatives that constrain the content that has to be covered and the nature of possible representations. These decisions have a ripple effect by defining, or in other ways, constraining, instructional moves and other pedagogical decisions. So it may be inappropriate to see knowledge of technology as being isolated from knowledge of pedagogy and content. In contrast to the simple view of technology (Figure 3 ), our framework (Figure 4 ) emphasizes the connections, interactions, affordances, and constraints between and among content, pedagogy, and technology. In this model, knowledge about content (C), pedagogy (P), and technology (T) is central for developing good teaching. However, rather than treating these as separate bodies of knowledge, this model additionally emphasizes the complex interplay of these three bodies of knowledge. We do not argue that this TPCK approach is completely new. Other scholars have argued that knowledge about technology cannot be treated as context-free and that good teaching requires an understanding of how technology relates to the pedagogy and content (
One of the most popular frameworks over the last decade is the Technological Pedagogical And Content Knowledge (TPACK) framework REF .
Technological pedagogical content knowledge: A framework for teacher knowledge
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