To improve physical and mental health, adolescents are recommended to engage in regular exercise. However, the majority is insufficiently active, often due to a lack of motivation. Hence, physical education (PE) teachers are encouraged to adopt motivating interaction styles and avoid being controlling. Teacher control is detrimental to students, even with occasional occurrences. However, we insufficiently know when PE teachers become controlling, what the long-term effects are, and what can be done to prevent it. Hence, we aim to examine reciprocal teacher-student interactions and develop and evaluate an intervention to prevent controlling teaching. First, we will observe moment-to-moment interactions between teacher control and students’ behaviours during a class, and examine longitudinal associations between teacher control and students’ motivational, behavioural, and well-being variables during a school year. Later, we will train PE teachers' competences to prevent controlling teaching via ecologically valid simulation-based learning environments using virtual reality and evaluate its effects on teacher control and student outcomes in an RCT.