There isn’t a valid one because the construct of “distance education” is meaningless. Sure, Keegan has a nice list of diagnostic characteristics. Kearsley avoids the question. The Commission on Colleges Southern Association of Colleges and Schools defines it “for the purposes of accreditation review, as a formal educational process in which the majority of the instruction occurs when student and instructor are not in the same place. Instruction may be synchronous or asynchronous. Distance education may employ correspondence study, or audio, video, or computer technologies (see Morehead’s statement).” But each of the definitions is flawed by one basic assumption — that there is a distinction between distance and non-distance education.
Pick a definition. Examine the parts. Each one is silly. Differentiation becomes an exercise in the arbitrary selection of media, channel, and message. We’ll continue to use the term Distance Education in the course and by that phrase, we’ll mean All Education. The key in designing educational experiences — and in helping students engage in productive learning — is understanding that the goal is independant of the means. I want you all to learn how learning and education relate to each other so that you can make effective technology choices and use good techniques in your teaching.
And while I’m on the subject of definitions
There is no such thing as distance learning. Learning is the process of assimilating a body of knowledge for application in a personal – or organizational – context. You learn by making things part of you. If it’s part of you, how can it be distant?