This is not invariably so and some programmes have operated on too small a scale to yield economies. A major economic advantage of distance education is that it does not require lengthy full-time residence at a college. There are, however, limits to the economies that can be obtained if quality and effectiveness are to be assured by student support and the supervision of classroom practice. In some cases, the favourable economic evidence on distance education reflects the relatively high cost of conventional teacher education. The major factors affecting the cost of distance education are the number of students and options within the programme, the sophistication of the teaching media used, the arrangements for student support and the supervision of classroom practice, and the success rate.
Limited data are available on the costs of different media.
The research that has been undertaken makes it possible to identify four characteristics of a successful programme. These are likely to have obtained a good balance between the various different elements in teacher training and an integration between them. Within that balance, there needs to be an adequate emphasis on teaching practice. Assessment systems need to reward the qualities that are seen as important within the programme. Programmes are likely to benefit from the use of a combination of different teaching media.