Students repeatedly chose between brief reinforcement (cartoon viewing) followed by a long time-out and extended reinforcement followed by a brief time-out. They infrequently chose the former schedule, which they rated as "unpleasant." Then they were instructed to choose only this subjectively aversive schedule. When participants were informed that leaving would not interfere with the research and that most participants had left, the proportion of participants who withdrew rose across weeks of the semester, with later sign-ups quitting at more than twice the rate of early sign-ups. When normative information was omitted, the withdrawal rate was negligible. The time-of-semester trend for withdrawals broadens previous findings showing performance deficiencies on repetitive, aversive tasks in participants who sign up later in the semester. (Contains 2 tables and 3 figures.)