Is the way that kindergarteners view their willpower – as a limited or as a non-limited resource – related to their motivation and behavioral self-regulation? This study is the first to examine the structure of beliefs about willpower in relation to behavioral self-regulation by interviewing 147 kindergarteners (52% girls) aged 5 to 7 years (M = 6.47, SD = 0.39). A new instrument was developed to assess implicit theories about willpower for this specific age group. Results indicated that kindergarteners who think of their willpower as a non-limited resource showed better behavioral self-regulation than children who adopted a more limited theory, even when controlling for age and gender. This relation was especially pronounced in low achieving children. Mediation and moderation analyses showed that this relation was partly mediated through the children’s willingness to invest effort to reach a learning goal. Findings suggest that fostering metacognitive beliefs in children, such as the belief that willpower is a non-limited resource, may increase behavioral self-regulation for successful adjustment to the demands of kindergarten and school.