Being able to assess one's own performance would seem to be prerequisite to most forms of self-management. The present study investigated the extent to which children in a typical second-grade classroom could accurately assess their own academic on-task behavior. In essence, this investigation replicated an experiment by Glynn and Thomas (Journal of Applied Behavior Analysis, 1974, 7, 299–306) and extended those findings, by studying self-assessment over a longer span of time. The 31 children in the class ranged in age from 7 yr five months to 8 yr six months. Although only eight “problem” children were observed and studied, the self-control treatment procedures were applied to all children in the class. Behavior was observed daily during mathematics lessons for over eight school weeks. The study utilized a five-phase ABABC design, where the A phases were baseline periods, B phases were self-control periods, and C phase was a postcheck. In the self-control phases, children were asked by the teacher to put a check on their own individual performance card if they were on-task when a signal sounded. If they were not on-task, they were instructed not to touch their card. Typically, 15 to 20 signals occurred per 40-min session. At the end of the lesson, children were allowed to choose games to play according to how many checks they had earned. During all experimental phases, observers measured children's on-task behavior. Other observers measured the children's accuracy of self-assessment in the self-control phases. The results showed noticeable increases in the daily mean on-task behavior scores in the self-control phases following baseline phases. Also, a high level of on-task behavior was maintained in the postcheck phase. The variances of on-task behavior scores during the self-control phases were noticeably smaller than those in the baseline phases. Generally, individual data reflected group results, with some minor differences. Levels of accuracy of self-assessment varied from very accurate (95% of the time) to relatively inaccurate (56% of the time). The overall level of accuracy for all children was 78%. No consistent individual pattern appeared across phases. Some children got better as the study proceeded and some got worse. Most subjects tended to give themselves too much reinforcement, rather than too little. Peer social surveillance appeared to be the major factor that influenced individuals' evaluation of their own behavior, even though the teacher did make some control remarks in regard to how the children marked their cards. The results also demonstrated that self-control techniques can increase on-task behavior in a classroom with no history of external reinforcement, and that these techniques can have a lasting effect for more than two months of a school year.