This article explores pre-service and in-service science teachers' perceptions on active learning, and examines the effectiveness of active learning by pre-service science teachers in the Irish second level classroom through a two-phase study. In the first phase, data on perceptions were gathered from final year pre-service teachers and in-service teachers in Irish post-primary schools. In the second phase, pre-service science teachers, working with teacher educators, designed a comparative test for students in lower secondary science classrooms. This tested achievement differences for students taught in traditional ways and students taught using active learning approaches. While the test results show a significant difference between traditional teaching and active learning, overall analysis indicates that the majority of teachers in the study were not convinced of the value of this way of teaching. The findings have implications for science teaching and the enactment of curriculum reform measures in compulsory education.