The major purpose of this study was to describe the rule-governed and contingency-shaped behavior of learning-disabled, hyperactive, and nonselected elementary school children working on a computer-managed task. Hypotheses tested were (1) that the children would differ in the degree to which either instructions or external contingencies controlled their behavior, with the hyperactive children being more sensitive to external contingencies, the learning disabled children more sensitive to instructions, and the nonselected children responding somewhere between; and (2) that the hyperactive children would show more response inconsistency and inappropriate responding than the other two groups. Ranging in age from 94 to 132 months, subjects were 20 referred hyperactive and/or attention deficit disordered children, 20 second- and fourth-grade learning disabled children, and 20 second- and fourth-grade nonselected children. Ten nonselected kindergarten children were involved in a concurrent developmental comparison study. Results revealed no interactions of diagnosis or grade with type of instructions. However, a fine-grained analysis of task performance yielded variables which discriminated grade levels and diagnostic categories. (RH)