Background/Context: High schools are under increasing pressure to move beyond just graduating students, and many high schools today continue to have low rates of student retention and learning, particularly for students from traditionally low-performing subgroups. Differential dropout rates, wherein low-income students, minorities, and English language learners leave school at higher rates than other students, only compound the problem. Purpose/Objective: In this study, we examine differences in instructional quality between two higher and two lower value-added high schools, as measured by the Classroom Assessment Scoring System-Secondary (CLASS-S). It explores (a) differences in levels of instructional quality, (b) differences in the proportions of students taking advanced courses, and (c) differences in the way teachers think and talk about their classroom challenges. Research Design: This is a mixed methods study that combines data from classroom observation protocols with teacher interview data. We use multilevel statistical models to address the first two research questions and emergent, inductive coding to determine commonalities within schools in how teachers implement higher-quality instructional practices. Findings/Results: We find that the average difference in instructional quality, as measured by the CLASS-S, was not very wide across our four case study schools and that the biggest differences were between the two higher value-added high schools. Our interview data suggest that teachers in the two higher value-added schools are more proactive about providing emotional support and preventing behavioral problems, and intentional about attending to content and engaging students in higher-order thinking. Conclusions/Recommendations: The lack of variation in classroom instructional practice across schools also suggests the need to attend to the ways that schools support academic learning outside of the classroom. Qualitative findings signal that the quality of classroom instruction is not the only critical input to students' learning gains when trying to identify what leads schools to place highly in value-added rankings.