Young children often struggle to accomplish goals without instructions or reminders from adults. Less-structured activities might facilitate children’s emerging self-directed executive functioning, by giving children opportunities to choose what to do and when, and to practice setting and accomplishing goals. In one study, 6-year-old children who spent more time in less-structured activities showed better self-directed switching on a verbal fluency task; conversely, more time in adult-structured activities predicted worse switching (Barker et al., 2014). However, it is unclear from such correlational studies whether children’s activities caused differences in executive functioning, as opposed to differences in executive functioning shaping how children spent time, or a third factor driving both. The current study thus investigated relationships between children’s experiences and self-directed executive function in a genetically-informative longitudinal twin sample (N= 936; 472 female, 464 male) . Twins who lived in more structured homes and participated in more structured activities at ages 3 and 4 showed worse self-directed switching on a verbal fluency task at age 7, controlling for earlier performance and concurrent levels of environmental structure. These relationships persisted controlling for general cognitive ability, vocabulary knowledge, and socioeconomic status. Associations between early time use and self-directed switching were mediated by nonshared environmental rather than genetic factors. These findings are consistent with early structured time causally affecting later self-directed executive function.