Research on the educational value of play tends to focus on active players, especially when evaluating novel interaction technologies. However, a long history of scholarship underscores observing communal practice as a primary means of enculturation and learning. This paper demonstrates learning opportunities available within a range of participation forms--from spectator to player and some in between--that emerge around "Geometris," a collaborative, body-scale geometry game, as installed in a children's science museum. Considering learning as participation in communal practice, I present frequency analysis of roughly 350 participants followed by thick narrative descriptions of 3 focal groups to characterize the learning opportunities available within diverse forms of participation in this technologically enabled gameplay. I also identify particular design elements--namely the user-agnostic input mechanism and certain crowd control measures--that inadvertently enabled these participation forms. Theoretical implications include the pedagogically relevant range of action-perception possibilities available across participation forms. Additionally, proposed design heuristics could facilitate these diverse forms of participation in other educational designs.