In science education, students sometimes create and engage in spontaneous science-oriented play where ideas about science and scientists are put to use. However, in previous research, little attention has been given to the role of informal spontaneous play in school science classrooms. We argue that, in order to enhance our understanding of learning processes in school science practices, research that investigates play as an aspect of everyday culture is needed. The aim of this paper is to explore students' informal play as part of activity in lower secondary school science. The empirical study was conducted in two Swedish compulsory schools in grade 6. Data were collected throughout a teaching unit called "The Chemistry of Food" during a 10-week period using video and audiotape recordings of classroom work. Our analyses show that the play students engage in involves the transformations of given tasks. We find that students' spontaneous collective play offers opportunities for them to explore the epistemic values and norms of science and different ways of positioning in relation to science. Our findings contribute to the understanding of how learning in the school science classroom is socially and culturally--historically embedded and how individual students' engagement through play may transform and transcend existing classroom practices.