Under the Every Student Succeeds Act (ESSA), evidence-based interventions are practices or programs that have evidence showing they are effective at producing results and improving outcomes when implemented; a promising intervention should be supported by one or more correlational studies with controls for selection bias. A goal of this research was to meet tier 3 ESSA standards by analyzing the impact of Classworks intervention while controlling for selection bias. This report analyzes the performance of 15,000 students on Renaissance® Star math and reading assessments. Students who received Classworks instruction outperformed students without exposure to Classworks instruction by significant margins.