The project was designed to extend previous research examining whether the benefit of contextual interference differs depending on the amount of practice completed. It has generally been found that when adults attempt to learn several movement tasks within the same practice session, they learn the tasks better when practice is randomized (so that practice of the tasks is presented in an unpredictable order) than when it is blocked (so that all practice of one task is completed before practicing the next) (Brady, 1998). However, the improved learning seems to be dependent on how the movements to be learned differ with respect to each other. When the tasks differ only in overall duration, research has been equivocal about whether any benefit exists for practicing the tasks in a random order. Smith and Penn (1999) suggested this was because the benefit of random practice would only emerge after prolonged practice at the tasks, and that where research had not found a difference, it was because insufficient practice had been provided. To support this contention, Smith and Penn (1999) had participants practice a movement at three different durations across two practice sessions. Improved learning of the task in random practice relative to blocked practice conditions did not emerge until after the second practice session. However, this finding may have been at least partially due to participants having completed retention tests after both their first and second practice sessions, or to practice being completed over two days (Shea, Lai, Black, & Park, 2000). This study removed these confounds by having participants (n=48) practice three variations (fast, medium, slow) of a timing task for either 135 trials or 270 trials (all trials completed in one session and in one day), in either a blocked or serial order. The single practice phase was followed 24 hr. later with a 30 trial retention phase. Total error (E) was derived for measures of relative timing and overall duration error, across both acquisition and retention phases. While the relative timing analysis showed only a general improvement from the first to the second retention phase, the overall timing analysis found a significant cross-over interaction between retention phase and practice type. These results are similar to those of Smith and Penn (1999), and suggest the earlier results were not limited to the number of practice sessions or the number of days over which practice was spread. Keyword(s): performance, research, technique