The study investigated the manner in which locus of control (the degree to which an individual conceptualizes a relationship between his own behavior and the outcomes of this behavior) interacted with selected task and reinforcer variables in the performance of educable mentally handicapped boys. One hundred ninety-two adolescent males performed each of four tasks in four different reinforcement conditions. It was suggested that tasks themselves, as well as reinforcers, provided information to the individual concerning his behavior. Results were interpreted as generally supporting the hypothesis. Implications were drawn for the use of reinforcers in the classroom, the role of task interest in curriculum design, and the need to consider individual differences in motivational orientation when selecting instructional materials and methods. (CD)