This paper presents a research-based teaching-learning sequence (TLS) that focuses on the notion of interaction in teaching Newton's third law (N3 law) which is, as earlier studies have shown, a challenging topic for students to learn. The TLS made systematic use of a visual representation tool--an interaction diagram (ID)--highlighting interactions between objects and addressing the learning demand related to N3 law. This approach had been successful in enhancing students' understanding of N3 law in pilot studies conducted by teacher-researchers. However, it was unclear whether teachers, who have neither been involved with the research nor received intensive tutoring, could replicate the positive results in ordinary school settings. To address this question, we present an empirical study conducted in 10 Finnish upper secondary schools with students (n = 261, aged 16) taking their mandatory physics course. The study design involved three groups: the heavy ID group (the TLS with seven to eight exercises on IDs), the light ID group (two to three exercises on IDs) and the no ID group (no exercises on IDs). The heavy and light ID groups answered eight ID questions, and all the students answered four questions on N3 law after teaching the force concept. The findings clearly suggest that systematic use of the IDs in teaching the force concept significantly fostered students' understanding of N3 law even with teachers who have no intensive tutoring or research background.