<p>Shaping involves the reinforcement of successive approximations toward a terminal response. Historically, shaping has been described as an art as much as a science, but there are also mathematical approaches to shaping. One such approach is the use of a percentile schedule. Percentile schedules allow a teacher to account for recent behavior and select a criterion to control the amount of exposure to extinction. Although percentile schedules have proven an effective means of shaping academic responding under some conditions, the parameters have not been extensively investigated, and they have not been directly compared to other variations of shaping. In the current study, we evaluated two parameters of a percentile schedule and another variation of shaping for increasing academic engagement for three students attending an Extended School Year program. Neither arrangement of a percentile schedule consistently increased academic task completion for students in the current study. Shaping, particularly when it started with a response that did not resemble the final performance, was more effective. Overall, the results of the current study suggest that there may be barriers to using percentile schedules with some students. For instance, the percentile arrangements in the current study may have been ineffective for two participants due to insufficiently variable behavior during baseline, which limited systematic changes in the criterion. Some students may require supplemental techniques to increase the likelihood of engaging in the next successive approximation, such that it can be captured by the delivery of an effective reinforcer and allow continued progression of the criterion over time. Because shaping procedures necessarily varied across participants, conclusions about the effects of percentile schedules in isolation are limited in this study.</p>