Instructional aids - charts, models, maps, specimens, slides, films, computers and the rest - are used by the teacher to clarify concepts.

The reason is that many ideas are abstract or otherwise inaccessible in words alone. A model of the heart shows a structure that no verbal description conveys as clearly; a map fixes a spatial relationship at once; a working model of a pulley makes a principle visible in operation. Aids also bring into the classroom what cannot physically be brought there - a distant place, a microscopic organism, a historical event, a process too fast or too slow to observe directly. And because they engage sight and sometimes hearing and touch alongside words, they leave a stronger impression than words alone, which is the basis of Dale's Cone of Experience: the more direct and concrete the experience, the more is retained.

Attracting the students is the closest distractor and is a real secondary benefit - aids do rouse interest and hold attention, and a class is more alert when something is being shown. But interest is a means rather than the end. An aid that attracted attention while conveying nothing would have failed, and this is precisely the criticism made of aids used for their own sake.

Glorifying the class suggests decoration, which is not an educational purpose at all. Charts left on a wall as ornament are not instructional aids in use.

Ensuring discipline may follow incidentally, since engaged learners are less disruptive, but discipline is a by product and not the reason an aid is chosen.

The governing principle is that an aid is a means to an end. It supports the teacher rather than replacing the teacher, and it should be selected for its fit with the concept being taught.

Hence instructional aids are used to clarify the concepts.