Context: Policy makers have long used policy tools to influence various components of the education system. The passage of No Child Left Behind increased the federal role and the focus on student outcome measures. This change in the policy environment can affect not only teachers and teaching but researchers and research on teaching as well. Purpose: This article examines ways in which the current policy context influences teaching and explores the challenges these influences pose for research on teaching. To illustrate this potential policy impact, we focus on three core dimensions of teaching: who is the teacher, is teaching practice stable or changing, and what constitutes teaching quality. Research Design: We draw on our High-Quality Teaching study of fourth- and fifth-grade reading and mathematics instruction. For this article, we analyzed classroom observation data, teacher logs of curriculum coverage, and focus group interviews with school personnel. We pay particular attention to changes in instruction over time and in different contexts. Conclusions: Although we anticipated that policy pressures might influence conceptions of teaching quality, we were surprised by the scope of these influences. Our findings indicate underreported, multiple influences on student learning due to both local and federal policies; unexpected changes in what is taught and in what kind of teaching occurs within the school day, throughout the year, and across years; and narrowing conceptions of teaching quality. Policy influences on these core dimensions challenge researchers to specify more carefully who is responsible for teaching whom, maintain flexibility in data collection, retain research participants across years, and examine alternative conceptions of quality teaching.