The expectations we hold of other people can act as self-fulfilling prophecies. A major component of research on interpersonal expectancy effects addresses the behavioral processes underlying this phenomenon. How are perceivers' expectations communicated to targets so as to create a self-fulfilling prophecy? Oddly, although expectancy mediation has been such a major question in this area of research, it remains the most glaring gap in our knowledge, especially at the theoretical level.

The problem is not that data on expectancy mediation do not exist; most studies in this area address mediation to some extent. Rather, as Bob Rosenthal and I noted in our meta-analysis of the mediation literature, the great weakness was the lack of a coherent, theoretically meaningful organization of the mediating behaviors that had been studied, as well as a lack of understanding of how the mediators fit into the wider expectancy process (Harris & Rosenthal, 1985). With the exception of Rosenthal's (1989) affect-effort theory of expectancy mediation, practically nothing had been done since 1985 to remedy these weaknesses.

The major obstacle to developing a comprehensive theory of expectancy mediation is that the behaviors exhibited by perceivers will necessarily depend on the situational context and the nature of the expectancy manipulation. The mediation of teacher expectancy effects will be different from the mediation of expectancy effects in a getting-acquainted situation, because the role demands and situational constraints for the two contexts differ.