This paper discusses the findings of an evaluative and interpretive study into the potential of in-service education to improve science education in Swaziland. Short-term and long-term effects of an in-service intervention are evaluated in terms of changes in classroom processes. The teaching approach of participating teachers has been monitored and analysed before, during and 1 year after the in-service intervention, to assess whether changes occurred. The study revealed the subjective interpretations of teachers about those changes, also in relation to contextual factors. Recommendations are put forward to enhance the potential of in-service education in comparable contexts. (Contains 7 tables, 1 figure, and 3 notes.)