People often perseverate, or repeat habitual behaviors when they are no longer appropriate. For example, after sorting cards by one rule, children will reliably perseverate with this rule even when they are clearly and repeatedly instructed to switch to a new rule. Such perseveration may result from limitations in working memory abilities for holding instructions actively in mind. If so, children may switch more readily to a new rule following experiences that are less demanding on working memory, such as guided practice with the new rule. In a study testing this prediction, 3-year-old children received direct instructions to switch to a new rule, guided practice with the new rule, or both. Providing children with guided practice was much more effective than telling them what to do. These findings support theories of perseveration based on competing memory systems, challenge alternative theories, and suggest effective methods for countering prepotent behaviors.