This study draws on data from a 10-month critical narrative inquiry of science teaching and learning in a third grade, dual language, integrated co-teaching classroom. The teachers were participants in a 14-week science professional development seminar that enrolled inservice and preservice teachers and focused on enhancing science teaching and learning in the classroom while drawing on the unique resources of the city. Data for the study include classroom audiotape, student work samples, audiotape of teacher planning meetings, semi-structured interviews, and a team portfolio. Data were analyzed using constant comparative methods. The findings illustrate a dialectical relationship between agency and structure and show a transition from more structurally reproductive toward more structurally transformative teacher agency over time. The emphasis on literacy in the school, the dual language program, and teachers' lack of science content knowledge tended to promote structurally reproductive agency, whereas the teachers' participation in a science professional development program and the unique context of a museum climate change exhibit fostered more structurally transformative teacher agency. Student agency was greatest when teachers engaged in more structurally transformative forms of agency.