In an attempt to explain the evidence which indicates that internal perception of control is positively related to academic achievement, this paper suggests that mediating motivational and cognitive reactions, which differentiate internals from externals, may account for this relationship. Furthermore, on the basis of data which suggest that the perception of locus of control is a changeable disposition, this paper calls for structuring environments that will induce and maintain realistic internal perception of locus of control. A literature review on the relationship between locus of control (LOC) and academic achievement revealed that more internal beliefs are associated with greater academic achievement and that the magnitude of this relation is small to medium. Characteristics of the participants in the reviewed studies and the nature of the LOC and academic achievement measures were investigated as mediators of the relation. The relation tended to be stronger for adolescents than for adults or children. The relation was more substantial among males than among females. Stronger effects were associated with specific LOC measures and with standardized achievement or intelligence tests than with teacher grades.