Undergraduates participating in experiments late in the semester generally perform more poorly on demanding tasks and withdraw more often than those participating early. To investigate effects of task aversiveness, some participants were instructed to choose brief cartoon reinforcement with a long time-out while others were instructed to choose longer cartoon reinforcement with a short time-out. Three times as many students withdrew under the unfavorable schedule but withdrawal rates were significantly higher at the end of the semester under both conditions. The Zimbardo Time Perspective Inventory (Zimbardo & Boyd, 1999) marginally predicted task persistence. Numerous end-of-semester obligations appear to promote withdrawals independently of task aversiveness. (Contains 4 figures.)