Although a growing number of young people are choosing to undertake non-compulsory education, there is concern that not enough are electing to study science, technology, engineering and mathematics subjects. Research has suggested that out-of-school science activities, research participation and a child’s family interest can increase both knowledge of and interest in science, resulting in a higher likelihood of studying a science, technology, engineering and mathematics subject at an advanced level. However, the majority of research to date has been conducted with secondary school-age students. This study investigated the impact of Summer Scientist Week, an annual out-of-school science engagement event for 4–11-year-olds and their families held at the University of Nottingham, UK. This event introduces primary school-age children to psychology-related research and activities about the mind and brain. Findings from interviews conducted with children and parents at the event, as well as survey data from previous attendees aged 14–17 years, indicated an increase in knowledge and interest in science that was maintained over several years, influencing choices in A-level subjects. This is the first study to demonstrate the positive impact of out-of-school science activities in primary school-age children, and its sustained influence on later academic choices in secondary school.