Age-appropriate modifications of the A-not-B task were used to examine 2-year-olds' search behavior. Several theories predict that A-not-B errors will increase as a function of number of A trials. However, the hierarchical competing systems model (Marcovitch & Zelazo, 1999) predicts that although the ratio of perseverative to nonperseverative errors will increase, the likelihood of perseveration will be an inverted U-shaped function. In Experiment 1, children received 1, 6, or 11 A trials in a multistep multilocation search task. In Experiment 2, children received 3, 7, 11, or 15 A trials in a sandbox task. Results from Experiment 1 showed that the ratio of perseverative to nonperseverative errors increased with number of A trials, and results from both Experiments 1 and 2 indicated that the likelihood of perseverative errors was highest following a moderate number of A trials. These findings are consistent with the suggestion that search behavior provides an index of the development of conscious control. (Contains 4 figures, 2 tables and 4 footnotes.)