Field experience can be a rich site for prospective teachers to develop the knowledge and skills they need for effective teaching, however little is known about how structures for supporting interactions between mentor and prospective teachers can maximize prospective teachers' learning. Lesson study has been shown to enhance practicing teachers' mathematical knowledge for teaching through collaborative inquiry with their peers. In this paper, we discuss the use of mentor-guided lesson study to support mentor and prospective teachers' collaboration in the field and provide evidence showing its potential to strengthen prospective teachers' mathematical knowledge for teaching. We will also share insights from the field for those interested in implementing this activity in teacher preparation coursework. [For the complete proceedings, see ED584443.]