Science learning is most often examined within formal education contexts, even though students spend more of their lives outside of the classroom. Students may interact with scientific phenomena during these out-of-school experiences, providing additional opportunities for learning to take place. Prior studies have found that optional science experiences have positive effects on science knowledge and attitudes. However, these studies do not always account for initial differences between students who are able to participate in many optional experiences and those who cannot. Moreover, many studies focus on high-quality science programs, which may not be representative of the average out-of-school experience. Using a longitudinal dataset of 3,700 6th and 8th grade students in urban and suburban schools from two regions in the United States, the current study investigates the effects of typically occurring optional science experiences during the school year on the development of science knowledge and attitudes. Using propensity score matching, we matched participating and nonparticipating students for characteristics that drive self-selection into these experiences, then analyzed separately for effects of school-related versus home-related science learning experiences. Stable patterns across analytic models reveal growth in science attitudes with both school- and home-related science experiences, but a greater relative decline in science knowledge with school-related science experiences. Thus, typically occurring optional science experiences can influence students' attitudes and knowledge, but the effects can vary by the type of experience that students attend.