An undergraduate seminar was designed to help preservice teachers focus on students' learning. Preservice teachers planned and conducted weekly tutoring sessions with fourth graders and discussed their experiences in weekly discussions. The author investigated what preservice teachers learned about teaching mathematics from their focus on students' learning of mathematics. The author examined the tasks that preservice teachers posed to children, the questions they asked of children, and the reflections they wrote about their experiences. The article describes what the preservice teachers learned from their experiences and provides insights into their knowledge and skills for developing children's mathematical power. (Contains 3 tables and 2 figures.)