Responding to an Illinois law that took effect in 2010, the Performance Evaluation Reform Act (PERA), Chicago Public Schools (CPS) created and implemented the REACH (Recognizing Educators Advancing Chicago's Students) educator evaluation and support system. REACH was piloted in 2012-13. It is still being implemented as of the 2019-20 school year, and will continue to be implemented through June 2024, per the teachers' contract agreed upon in fall 2019. The evaluation system includes classroom observation ratings of teacher practice, as well as up to two student growth measures. This brief addresses the research question: What feedback did teachers report as most useful? The data and analysis that answer this question provide insights that may help district leaders, principals, and teacher-evaluators make the most of classroom observations and ultimately drive improved teacher practice, student experiences, and student outcomes. This brief is part of a series of three to extend previous research from the University of Chicago Consortium on School Research (UChicago Consortium) on early REACH implementation and the REACH evaluation system five years after the 2012-13 rollout. [For "Teacher Evaluation in CPS: REACH Ratings and Teacher Mobility. Research Brief," see ED608092. For "Teacher Evaluation in CPS: Perceptions of REACH Implementation, Five Years In. Research Brief," see ED608094.]