This study uses a regression discontinuity design to evaluate the impact of seventh-grade interventions delivered by 25 schools on the reading and school engagement outcomes of struggling readers. Students in participating schools were assigned to intervention (n = 1,495) or comparison (n = 4,397) conditions, based on their state reading performance and reading fluency scores in sixth grade. On the state reading test, intervention impact favoring the treatment group approached, but did not reach, statistical significance (p = 0.056, g = 0.15). On a measure of reading fluency, there was a significant interaction between the cut points schools chose for condition assignment and intervention impact (p = 0.015). In schools that chose a lower cut point, intervention students outperformed comparison students, while in schools that chose a higher cut point, comparison students outperformed intervention students. On a student self-report measure of school engagement, no significant differences between the intervention and comparison groups were observed (p = 0.83, g = 0.02). Implications for rigorous evaluation of interventions implemented by districts and schools under naturalistic conditions are discussed.