Spurred by concerns about an inadequately sized science, technology, engineering, and mathematics (STEM) workforce, there has been a growing interest in out-of-school time (OST) science activities as a means to foster STEM career interest. This study examines the association between OST science activities and STEM career interest in university through a logistic regression model and the calculation of prototypical odds ratios. The analysis addresses two main research questions: What is the correlation among different forms of OST activities? And, controlling for student demographic and background variables, what specific forms of OST activities are associated with STEM career interest in university? The study uses data from the "Persistence Research in Science and Engineering" survey (n = 6882), which employs a nationally representative sample of university students enrolled in introductory English courses. Results indicate that students' participation in OST activities, as well as their middle school interest in science and mathematics and their gender, plays a significant role in university career interest in STEM. Conclusions suggest that making OST clubs and competitions and the inclusion of non-fiction and science fiction within English Language Arts programmes may be beneficial to the development of students in STEM careers. Limitations include the paucity of research examining which students participate in these activities and what specific features or characteristics benefit them.