We present results of an experimental study of an urban, museum-based science teacher PD programme. A total of 125 teachers and 1676 of their students in grades 4-8 were tested at the beginning and end of the school year in which the PD programme took place. Teachers and students were assessed on subject content knowledge and attitudes towards science, along with teacher classroom behaviour. Subject content questions were mostly taken from standardised state tests and literature, with an 'Explain:' prompt added to some items. Teachers in the treatment group showed a 7% gain in subject content knowledge over the control group. Students of teachers in the treatment group showed a 4% gain in subject content knowledge over the control group on multiple-choice items and an 11% gain on the constructed response items. There was no overall change in science attitudes of teachers or students over the control groups but we did find differences in teachers' reported self-efficacy and teaching anxiety levels, plus PD teachers reported doing more student-centered science teaching activities than the control group. All teachers came into the PD with high initial excitement, perhaps reflecting its context within an informal learning environment.