Teachers are facing increasingly diverse classrooms globally. To support all students efficiently, teachers need to know their students. Drawing from the literature of teacher learning and inclusive education, we explored how teachers learn to know their students in a co-teaching context. Analysis of interviews and diaries of five co-teaching teams showed that teachers learned about their students in a co-taught classroom by observing students and by obtaining knowledge from and co-constructing knowledge with their co-teaching partner. Moreover, teachers' learning led to shared responsibility for the student and a better understanding of student diversity. Thus, sharing knowledge of students can lighten teachers' workload in inclusive settings and benefit both teachers and students.