This article examines a unique intervention in Chicago Public Schools (CPS) to uncover the causal impact on school performance of an evaluation system based on highly structured classroom observations of teacher practice. An iterative process of observation and conferencing focused on improving lesson planning and preparation, the classroom environment, and instructional techniques should drive positive changes in teacher practice. As teachers refine their skills and learn how best to respond to their students' learning needs, student performance should improve. Recent evidence from Cincinnati Public Schools confirms that providing midcareer teachers with evaluative feedback based on the Danielson Framework for Teaching observation system can promote student-achievement growth in math, both during the school year in which the teacher is evaluated and in the years after evaluation (see "Can Teacher Evaluation Improve Teaching?" research, Fall 2012).