Early experiences with planning and guiding children's learning can be exciting for preservice teachers in undergraduate teacher training programs. In this article, observations of a preschool play session guide four preservice teachers to design a series of play-centered lessons addressing serious science concepts (Hall 2010). While the concepts guided in these lessons are not new, identifying science thinking in children's play is valuable for preservice and inservice teachers as they plan learning opportunities that extend children's knowledge. This can be done by providing materials over long periods of time and using an engage, explore, reflect process, checking for understanding and relying on observations to guide long-term inquiry (Chalufour 2010). The assignment guiding this process asked preservice teachers to observe play, record their observations, then meet together to discuss and write their interpretations of the children's thinking. They were to use their interpretations to develop questions to plan for and guide a next play session.