Self-control performance may be improved by the regular practice of small acts of self-control. Ninety-two adults' self-control capacity was assessed using the stop signal paradigm before they started practicing self-control and again at the end of two weeks. Participants who practiced self-control by cutting back on sweets or squeezing a handgrip exhibited significant improvement in stop signal performance relative to those who practiced tasks that did not require self-control. Participants who did not practice self-control believed that the tasks should improved self-control, engaged in tasks that were effortful and made self-control salient, but did not actually require self-control. Supplemental analyses suggested that only practicing self-control built self-control capacity; the improved outcomes cannot be explained by self-fulfilling prophecies, increased self-efficacy or awareness of self-control. The results may have implications for understanding the development of self-control in both children and adults, as well as clinical implications for treating disorders that involve low self-control.