In the introduction to Chapter 4 we considered the paradox that the principles of reinforcement appear so simple, yet in real life behavior is often remarkably difficult to change. One explanation, we suggested, was that the principles of reinforcement might not be as simple as they first appear; in the course of that chapter, we encountered evidence supporting that view. Even brief delays of reinforcement, for example, have far more severe effects on learning than is commonly realized, and our understanding of phenomena such as motivation and stimulus control is still limited. Therefore, we could readily account for our difficulty in using reinforcement effectively by our incomplete understanding of the principles governing its use.

There is, however, another possibility. Even in those cases in which we do understand the principles of reinforcement, it can appear ineffective because we fail to apply the principles in a coherent and systematic way. That is, we might already know enough to use reinforcement more effectively, if only we would apply that knowledge systematically. This, at any rate, was the belief of several learning psychologists in the 1960s, and it led to a major effort, under the rubric of behavior modification, to apply the principles of reinforcement developed in the animal laboratory to practical problems of human behavior. In this chapter we will review some of these programs, considering the extent to which they have been successful, and, insofar as they have failed, what these failures can tell us about the remaining gaps in our knowledge. We will begin by looking at some of the attempts that have been made to apply the principles of reinforcement to education.