A peer-coaching approach was adopted in the out-of-class stage of the flipped classroom. Out of the classroom, learning tutors help students engage in learning and improve performance. Eighty-seven participants from two classes were involved in this study. One class of 44 students was the experimental group with the peer-coaching approach in a flipped classroom, and the other class of 43 students served as the control group learning by the conventional video-based flipped classroom mode. The experimental results revealed that peer coaching improved student engagement and interaction out of class. In the experimental group, students interacted not only with tutors and group peers but also with students from other groups. The experimental results also show that the proposed approach could improve students' learning achievements.