What is the best way to teach science? What kind of teacher training makes better science teachers? Donors now tend to fund in-service training (INSET) for teachers already in the classroom rather than pre-service teacher training. But what makes an effective INSET programme? And how can effectiveness be measured? Collaborative research by the Universities of York and Swaziland uses teacher perceptions and student learning outcomes to measure the effectiveness of an INSET programme for junior secondary science in Swaziland and asks whether the INSET methodology could be used in other subject areas.