In this study we focus on the effects of an intervention aiming to improve the English pronunciation skills of secondary school students in the Netherlands. In order to implement a new pedagogy successfully it is of the essence to take into account how teachers learn and what motivates them to adapt and change their way of teaching. Teachers need time to test and adapt a teaching design to fit the needs of their classroom practice and the students’ needs. In this paper the main focus is on finding evidence of teacher professional development in teaching English pronunciation. Results show that teachers are extrinsically motivated to change their teaching behaviour and classroom practice after using a computer assisted teaching tool to teach English pronunciation.