In the introduction to Teaching Machines and Programmed Learning: A Source Book (1960), a collection of articles penned by some of the best known theorists and practitioners in the field (including both Skinner and Pressey), A. A. Lumsdaine lists these as the three key properties of “teaching machines”:
First, continuous active student response is required, providing explicit practice and testing of each step of what is to be learned.
Second, a basis is provided for informing the student with minimal delay whether each response he makes is correct, leading him directly or indirectly to correction of his errors.
Third, the student proceeds on an individual basis at his own rate – faster students romping through an instructional sequence very rapidly, slower students being tutored as slowly as necessary, with indefinite patience to meet their special needs.
The devices thus represent a way of providing a pre-programmed study-practice combination which simulates, in partially or fully automated fashion, the functions of a private tutor in recitation and practice, with immediate correction of errors and feedback to the student.