Agreement on a constructivist theory of learning is not widespread due largely to what Derry (1996) terms "ethnocentrism within various constructivisms". At the same time, Ernest (1995) notes that, of seven paradigms of constructivism, the positions are all variants of radical constructivism. The outstanding consideration, however, concerns the need as Ernst sees it: "to accommodate the complementarity between individual construction and social interaction" (p.483). Whether knowledge is seen as socially situated or whether it is considered to be an individual construction has implications for the ways in which learning is conceptualized. From the radical constructivist perspective, how can their theory encompass both the collective activity and the individual experience to take into account the important classroom social interactions that are so much a part of the entire educational process? Such questions underlie the complexities involved in translating the diversity of perspectives into a common set of principles that can be operationalized. Yet, as Ernest claims in relation to the varying constructivist perspectives: "there is the risk of wasting time by worrying over the minutiae of differences" (p.459). Perhaps then, the optimal starting point for understanding the constructivist perspective to teaching and learning is to consider what constructivism is not.

Constructivism is often articulated in stark contrast to the behaviorist model of learning. Behaviorial psychology is interested in the study of changes in manifest behavior as opposed to changes in mental states. Learning is conceived as a process of changing or conditioning observable behavior as result of selective reinforcement of an individual's response to events (stimuli) that occur in the environment. The mind is seen as an empty vessel, a tabula rasa to be filled or as a mirror reflecting reality. Behaviorism centers on students' efforts to accumulate knowledge of the natural world and on teachers' efforts to transmit it. It therefore relies on a transmission, instructionist approach which is largely passive, teacher-directed and controlled. In some contexts, the term behaviorism is used synonymously with objectivism because of its reliance on an objectivist epistemology. Jonassen (1991) describes the assumptions of an objectivist approach to learning:

Objectivists believe in the existence of reliable knowledge about the world. As learners, the goal is to gain this knowledge; as educators, to transmit it. Objectivism further assumes that learners gain the same understanding from what is transmitted (...) Learning therefore consists of assimilating that objective reality. The role of education is to help students learn about the real world. The goal of designers or teachers is to interpret events for them. Learners are told about the world and are expected to replicate its content and structure in their thinking. (p.28)

This objectivist model has resulted in somewhat of a stereotyped portrayal of teaching and learning which is a widely criticized and often evoked as the target of educational reform. Susan Hanley, in an online discussion of constructivism, describes her perspective on the objectivist model:

Classes are usually driven by "teacher-talk" and depend heavily on textbooks for the structure of the course. There is the idea that there is a fixed world of knowledge that the student must come to know. Information is divided into parts and built into a whole concept. Teachers serve as pipelines and seek to transfer their thoughts and meanings to the passive student. There is little room for student-initiated questions, independent thought or interaction between students. The goal of the learner is to regurgitate the accepted explanation or methodology expostulated by the teacher. (p.3)

Where behaviorism emphasizes observable, external behaviours and, as such, avoids reference to meaning, representation and thought, constructivism takes a more cognitive approach. This subtle difference has profound implications for all aspects of a theory of learning. The way in which knowledge is conceived and acquired, the types of knowledge, skills and activities emphasized, the role of the learner and the teacher, how goals are established: all of these factors are articulated differently in the constructivist perspective. Within constructivism itself, authors, researchers and theorists articulate differently the constructivist perspective by emphasizing different components.

Nonetheless, there is some agreement on a large number of issues, for example, on the role of the teacher and learner. In von Glasersfeld's (1995b) radical constructivist conception of learning, the teachers play the role of a "midwife in the birth of understanding" as opposed to being "mechanics of knowledge transfer". Their role is not to dispense knowledge but to provide students with opportunities and incentives to build it up (von Glasersfeld, 1996). Mayer (1996) describes teachers as "guides", and learners as "sense makers". In Gergen's (1995) view, teachers are coordinators, facilitators, resource advisors, tutors or coaches. Understanding the role of the teacher in the constructivist classroom provides a useful vantage point from which to grasp how the theory impacts on practice:

The role of the authority figure has two important components. The first is to introduce new ideas or cultural tools where necessary and to provide the support and guidance for students to make sense of these for themselves. The other is to listen and diagnose the ways in which the instructional activities are being interpreted to inform further action. Teaching from this perspective is also a learning process for the teacher. (Driver, Aasoko, Leach, Mortimer & Scott, 1994, p. 11)

While the radical and social perspectives of constructivism each have their particular emphases, Ernest derives a set of theoretical underpinnings common to both:

1. Knowledge as a whole is problematized, not just the learner's subjective knowledge, including mathematical knowledge and logic.
2. Methodological approaches are required to be much more circumspect and reflexive because there is no "royal road" to truth or near truth.
3. The focus of concern is not just the learner's cognitions, but the learner's cognitions, beliefs, and conceptions of knowledge.
4. The focus of concern with the teacher and in teacher education is not just with the teacher's knowledge of subject matter and diagnostic skills, but with the teacher's belief, conceptions, and personal theories about subject matter, teaching, and learning.
5. Although we can tentatively come to know the knowledge of others by interpreting their language and actions through our own conceptual constructs, the others have realities that are independent of ours. Indeed, it is the realities of others along with our own realities that we strive to understand, but we can never take any of these realities as fixed.
6. An awareness of the social construction of knowledge suggests a pedagogical emphasis on discussion, collaboration, negotiation, and shared meanings (...). (p.485)

Central to constructivism is its conception of learning. Von Glasersfeld (1995) argues that: "From the constructivist perspective, learning is not a stimulus-response phenomenon. It requires self-regulation and the building of conceptual structures through reflection and abstraction" (p.14). Fosnot (1996) adds that "Rather than behaviours or skills as the goal of instruction, concept development and deep understanding are the foci (...) (p.10). For educators, the challenge is to be able to build a hypothetical model of the conceptual worlds of students since these worlds could be very different from what is intended by the educator (von Glasersfeld, 1996).

In this paradigm, learning emphasizes the process and not the product. How one arrives at a particular answer, and not the retrieval of an 'objectively true solution', is what is important. Learning is a process of constructing meaningful representations, of making sense of one's experiential world. In this process, students' errors are seen in a positive light and as a means of gaining insight into how they are organizing their experiential world. The notion of doing something 'right' or 'correctly' is to do something that fits with "an order one has established oneself" (von Glasersfeld, 1987, p. 15). This perspective is consistent with the constructivist tendency to privilege multiple truths, representations, perspectives and realities. The concept of multiplicity has important implications for teaching and learning:

...mathematics and science are viewed as systems with models that describe how the world might be rather than how it is. These models derive their validity not from their accuracy in describing the world, but from the accuracy of any predictions which might be based on them. (Hanley, 1994, p.4)

Multiplicity is an overriding concept for constructivism. It defines, not only the epistemological and theoretical perspective but, as well, the many ways in which the theory itself can be articulated. Researchers and theorists have developed variants of constructivism or have evolved the theory in different directions. Nonetheless, there are many common themes in the literature on constructivism which permit the derivation of principles, instructional models and general characteristics. The following section outlines how a constructivist epistemology and theory of learning may be expressed as or translated into a wide variety of specific characteristics or principles of constructivist learning and teaching.