This study investigated teachers' perceptions of the influences of action research on their thinking about instructional practices and the impact of this thinking on teaching practices. The four specific areas of investigation were teachers' perceptions about (a) the overall teacher role, (b) teachers' knowledge about teaching, (c) teaching practices, and (d) reflective practices. The data were collected from interviews with teacher researchers, informal classroom observations, and collection of teacher and student work and related artifacts. The data revealed that teachers perceived changes in the four areas of investigation. Engaging in the stages of action research provided teachers with a methodical structure for implementing and analyzing the teaching and learning process. This defined structure guided teachers through more systematic and conscious data collection, data analysis, and reflection.