Linguistic variation is a central concept in materials and methodology. The sequence of units is determined solely by principles of linguistic complexity. Sequencing is determined by any consideration of content, function, or meaning which maintains interest. The teacher controls the learners and prevents them from doing anything that conflicts with the theory. Teachers help learners in any way that motivates them to work with the language.
Language is created by the individual often through trial and error.
Accuracy, in terms of formal correctness, is a primary goal. Students are expected to interact with the language system, embodied in machines or controlled materials. Students are expected to interact with other people, eigher in the flesh, through pair and group work, or in their writings. The teacher is expected to specify the language that students are to use. The teacher cannot know exactly what language the students will use.