This study explored the impact of learning a new instructional practice in a US school district that places great value in a statewide student assessment. Grounded Theory methodology (Strauss & Corbin, 1998, Basics of Qualitative Research: Techniques and procedures for developing grounded theory, 2nd Edition, Sage Publications, Thousand Oaks, CA) was used to analyze interview and observation data from 20 teachers undergoing professional development in a new reading strategy. We found that teaching in a ''high-stakes'' assessment environment impacts the implementation, fidelity, and sustainability of new teaching methods. Most importantly, our results suggest that some teachers may use ''high-stakes'' assessments as their primary reference point in which to gauge the merit of innovative teaching practices. Furthermore, decisions regarding which components to implement, how often to use these components, and what materials to utilize in their implementation may be influenced by the preparation for and expected results of these tests.