Afterschool programs have increasingly gained attention as settings that can help enrich students' science learning. Even though science is widely included in afterschool activities, sites often lack adequate materials and staff know-how to implement quality science. To address this need, this article examines afterschool science in light of the National Research Council's comprehensive synthesis report on promoting science learning in informal environments (NRC, 2009). The author's present the results of their analysis of qualitative case studies of nine state-funded afterschool sites in California, discussing the strengths of these programs against the background of three key site-based constraints--time available for science, staff's science backgrounds, and instructional materials--as well as the importance of partnerships with outside organizations to support sites in overcoming these obstacles. The case studies were part of a larger study in which we surveyed 406 sites in a state-funded network of afterschool programs throughout California. The purpose of the survey was to collect data on sites' partnership networks and how partner support influenced the depth and frequency of science offerings. At various moments in our site observations, we saw science activities that engaged children in exploring phenomena, collecting and analyzing data, asking questions, and discussing scientific concepts. These observations provided "existence proofs" that afterschool settings can deliver effective science learning experiences. This finding is especially important in light of the reduced time being spent on science during the elementary school day. However, the cases also showed that the challenges programs face in providing science experiences prevent sites from pulling these experiences together into sustained and complete science learning. Having partnerships with other organizations is one way for programs to build their capacity for offering science.