We investigated the alignment between a teacher survey self-report measure and classroom observation measure of ambitious mathematics instructional practice among teachers in two urban school districts using two different standards-based mathematics curricula. Survey reports suggested mild differences in teachers' instructional practices between the two districts, whereas observation ratings indicated starker differences. That said, teachers' survey and observer ratings were significantly correlated in both districts. Factors significantly predicting the extent of survey-observation alignment included teachers' grade level, Mathematical Knowledge for Teaching, cognitive demand, and--for one district--teachers' adherence to the surface-level aspects of their curriculum. Qualitative analyses suggested that teachers' survey-observation alignment could be a function of their interaction with colleagues who provided instructional models against which they could gauge the extent of their standards-based instruction. Our study has implications for research on instructional practice, as well as for school district policies to support and evaluate teachers.