This study examines to what extent experienced teachers are aware of gender issues in the science classroom. It also explores how an introduction to gender theory might alter this awareness. Teachers wrote their reflections about a real classroom situation. They were then asked to analyse the same situation after having read texts that discussed gender theory concepts. The fourteen teachers' understanding about gender and society were challenged. Some teachers were able to analyse the case differently by applying gender theory, others discussed the case on a more general level, while one teacher showed signs of resistance regarding gender theory.