Extracurricular activities (ECA) are informal settings offering free-choice experiences that are generally voluntary, open-ended, non-sequential, self-directed, hands-on, and evaluation-free. This mixed methods study investigates participation in a high school science ECA by collecting the memories of former student members for their perceptions of engagement as well as social positioning. First, this study examines the levels in which the science club engaged these members, particularly females, in science and teaching. Second, the study also ascertains how participation in the club allowed members to explore new identities and fostered the development of new skills, actions and behaviors, expanding possible future trajectories of identification, specifically in science- and education-related career fields. Based on a review of the related literature regarding engagement and identity formation and the reconstructed reality from the memories of these students and sponsor, a theoretical framework has been constructed, based on seven essential elements of informal learning for an engaging as well as a socially constructive high school science ECA. The most significant findings are (1) the high correlation between engagement, specifically, cognitive engagement with social positioning, (2) the important role of emotional engagement in science ECA, (3) the major perception roadblocks to science learning that can be overcome, particularly for females in physical science, and (4) the importance of the teacher-student interactions in science ECA. Articulating a theoretical framework to legitimate the power of informal learning structures may help other educators to understand the potential benefits of science ECA and thus, increase opportunities for such experiential activities in order to enhance engagement and expand positioning of their students in science. More engaging, socially constructive science ECA have the potential to enhance science education. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]