This study evaluates the effects of a behaviour change intervention, which encourages the integration of PA into the teaching of academic lessons, on PA levels of students. The main outcome is mean minutes of moderate-to-vigorous physical activity (MVPA) daily generated during the intervention lessons. Teacher’s perceptions and students’ enjoyment of the programme were also evaluated. Students accumulated a mean of 8 minutes MVPA during the intervention lessons daily. The teacher and students were very satisfied with the programme. Therefore, changing teacher behaviour towards using physically active teaching methods is a promising way of increasing children’s PA levels.