Afterschool programs have garnered much attention as promising environments for learning where children can engage in rich science activities. Yet, little is known about the kinds of instructional materials used in typical, large-scale afterschool programs that implement science with diverse populations of children. In this study, we investigated the types, features, and use of science instructional materials at more than 150 public afterschool program sites across California. Using afterschool site survey data, we categorized the types and the range of materials used at the sites. We then collected a subsample of the instructional materials for in-depth analysis of their support features for enabling staff and children to enact science. We also interviewed afterschool site staff to better understand how they selected and used materials. Results from our analysis of survey and interview data show that afterschool staff primarily used stand-alone lessons and activities found on the Internet or in activity books as resources for planning and enacting science. Our analysis of the subsample of instructional materials indicate that curricular materials, while used less frequently by afterschool staff, have on average more of the support features that would help them implement high-quality science experiences with children.