The theoretical basis on which instructional models is based affects not only the way in which information is communicated to the student, but also the way in which the student makes sense and constructs new knowledge from the information which is presented. Currently, there are two opposing views which impact instructional design: symbol-processing and situated cognition (see Bredo, 1994, for a full description and comparison of these two approaches).

Until recently, the dominant view has been the traditional, information processing approach, based on the concept of a computer performing formal operations on symbols (Seamans, 1990). The key concept is that the teacher can transmit a fixed body of information to students via an external representation. She represents an abstract idea as a concrete image and then presents the image to the learner via a medium. The learner, in turn, perceives, decodes, and stores it. Horton (1994) modifies this approach by adding two additional factors: the student's context (environment, current situation, other sensory input) and mind (memories, associations, emotions, inference and reasoning, curiosity and interest) to the representation. The learner then develops his own image and uses it to construct new knowledge, in context, based on his own prior knowledge and abilities.

The alternative approach is based on constructivist principles, in which a learner actively constructs an internal representation of knowledge by interacting with the material to be learned. This is the basis for both situated cognition (Streibel, 1991) and problem-based learning (Savery & Duffy, 1995). According to this viewpoint, both social and physical interaction enter into both the definition of a problem and the construction of its solution. Neither the information to be learned, nor its symbolic description, is specified outside the process of inquiry and the conclusions that emerge from that process. Prawat and Floden (1994) state that, to implement constructivism in a lesson, one must shift one's focus away from the traditional transmission model to one which is much more complex, interactive, and evolving.

Though these two theories are totally different in nature, effective designers usually start with empirical knowledge: objects, events, and practices which mirror the everyday environment of their designated learners. Then, with a firm theoretical grounding, they develop a presentation which enables learners to construct appropriate new knowledge by interacting with the instruction. To quote the AI researcher, Herbert A. Simon, "Human beings are at their best when they interact with the real world and draw lessons from the bumps and bruises they get" (Simon, 1994).

Schlosser and Anderson (1994) refer to Desmond Keegan's theory of distance education, in which the distance learning system must artificially recreate the teaching-learning interaction and re-integrate it back into the instructional process. This is the basis of their Iowa Model: to offer to the distance learner an experience as much like traditional, face-to-face instruction, via intact classrooms and live, two-way audio-visual interaction. In contrast, the Norwegian Model has a long tradition of combining mediated distance teaching with local face-to-face teaching (Rekkedal, 1994).

Hilary Perraton (1988) defines the role of the distance teacher. When, through the most effective choice of media, she meets the distance students face-to-face, she now becomes a facilitator of learning, rather than a communicator of a fixed body of information. The learning process proceeds as knowledge building among teacher and students. (See Scardamalia and Bereiter, 1994, for an example of electronic knowledge building discussions.)

Distance education systems now involve a high degree of interactivity between teacher and student, even in rural and isolated communities separated by perhaps thousands of miles. The Office of Technology Assessment stresses the importance of interactivity: distance learning allows students to hear and perhaps see teachers, as well as allowing teachers to react to their students' comments and questions (US. Congress, 1988). Moreover, virtual learning communities can be formed, in which students and researchers throughout the world who are part of the same class or study group can contact one another at any time of the day or night to share observations, information, and expertise with one another (VanderVen, 1994; Wolfe, 1994).

At the elementary and middle school levels, distance learning usually takes the form of curriculum enrichment modules and ongoing telecommunications projects. Some examples of current projects are: De Orilla a Orilla, National Geographic Kids Network, Biomes Exchange Project, Earth Lab, Ask Professor Math, and AskAScientist (Barron, Hoffman, Ivers, & Sherry, 1994; US. Congress, 1988). Other modules are television-based, with the teacher as facilitator. Students work in collaborative groups, using manipulatives and hands-on activities in a distance learning environment (Pacific Mountain Network, 1994).

At the secondary level, locally or federally funded distance education addresses the needs of small rural school districts or underserved urban school districts. Some secondary school students may enroll in courses to meet graduation requirements which their own districts are unable to offer; some take advanced placement, foreign language, or vocational classes; others may be homebound or disabled. In many instances, talented or gifted high school students have been selected to attend distance classes because of their high academic ability and capacity for handling independent work. This makes classroom management easier, but it may disenfranchise students who lack discipline or time management skills. The resulting inequity of access then becomes a policy problem, not a technology problem.

Although technology is an integral part of distance education, any successful program must focus on the instructional needs of the students, rather than on the technology itself. It is essential to consider their ages, cultural and socioeconomic backgrounds, interests and experiences, educational levels, and familiarity with distance education methods and delivery systems (Schamber, 1988). Students usually adapt more quickly than their teachers to new technology. On the other hand, teachers who have begun to feel comfortable with the equipment don't mind having their students teach them new tips and tricks (Apple Classrooms of Tomorrow, 1992). The most important factor for successful distance learning is a caring, concerned teacher who is confident, experienced, at ease with the equipment, uses the media creatively, and maintains a high level of interactivity with the students.