Despite the increasing attention to afterschool science programs, little is known about the conditions under which children likely engage in meaningful scientific practices, such as argumentation and scientific explanation in those settings. This analysis draws on X hours of video data collected of elementary-aged children (n = 4) during a 14-day after-school science program. Findings suggest students engaged in argumentation and evidence-based explanation when explicitly prompted to account for either observation from experiment or data collected for themselves in relation to big science ideas. Students drew extensively on everyday experiences to support their ideas but are limited in expanding their thinking. Implications for designing afterschool science programs are discussed.