In this article, the authors tested the hypothesis that first-year teachers could take up forms of ambitious pedagogy under the following conditions: 1) that reform-based practices introduced in teacher preparation would be the focus of collaborative inquiry throughout the first year of teaching, 2) that participants use analyses of their students’ work as the basis of critique and change in practice, and 3) that special tools be employed that help participants hypothesize about relationships between instruction and student performance. Eleven secondary science teachers engaged in tool-supported collegial analysis of their students’ work over two years, spanning pre-service and in-service contexts.