As a model for learning to teach, coteaching places two or more student teachers and cooperating teachers in a classroom. Effective coteaching requires coplanning, and this case study examines how six coteachers planned instruction for three environmental science classes. Using sociocultural theory, the study provides insight into the complexity and challenges in coplanning such as using collective knowledge to produce lesson plans, identification of teaching resources, the importance of communication between coteachers during planning and the enactment of lessons, and teachers' time as a limited resource. Coplanning provided learning experiences for student and cooperating teachers through reflective discussions that proposed ideal forms of practice and the alignment of teaching to achieve that goal.