There must not be even a hint that learning is hierarchial. Learning cannot be presented as an edifice constructed on a foundation. The learner must be allowed to enter in at any point. Entering in the middle should not make things more difficult for him or her. This is why you shall never hear or see a television program begin with the caution that if the viewer has not seen the previous programs, this one will be meaningless.
Television is a nongraded curriculum.
Television excludes no viewer for any reason. Television excludes no viewer at any time. In other words television does away with the idea of sequence and continuity in education.