Effects of a self-instructional training procedure on the on-task behavior of four mentally retarded young adults in a sheltered workshop were investigated using a multiple-baseline design across subjects. The subjects chosen had been identified as demonstrating a high incidence of off-task behavior for small assembly tasks such as stamping and stuffing envelopes, sorting mail by zip code, and collating printed material. Effects of the procedure on the rate and accuracy of task performance were recorded. Results indicated that mean on-task behavior of all four subjects increased an average of 74 percent over baseline performance, and generalized from the training to the workshop setting. A two-week followup check indicated that on-task behavior maintained over time. Supplemental recording indicated that rate of production did not increase substantially for any subject. (Author/JW)