Based on the Lexile® Framework, a scientific approach to reading and text measurement backed by more than two decades of ongoing research, Achieve3000®, a web-based differentiated reading program used by HISD, is designed to improve student reading ability and comprehension of increasingly complex texts by initially meeting students where they are academically. The present study focuses on cohorts of 9th and 10th graders and assesses the impact deriving from the use of Achieve3000's reading solutions on students' scale score performance on the State of Texas Assessments of Academic Readiness End-Of-Course (STAAR EOC) for the English I and English II exams. Utilizing the inverse-probability-weighted regression adjusted (IPWRA) estimation method to account for the non-randomness of student self-selection into Achieve3000 usage, the results of this evaluation may be viewed as causal. Findings suggest that students' use of Achieve3000's web-based software leads to higher performance on the STAAR EOC exams than non-use of Achieve3000. Controlling for student- and school-level factors, the treatment effect among 9th -grade Achieve3000 students was 50 scale score points higher than the potential outcome mean among their non-Achieve3000 peers on the English I assessment. The corresponding gain for 10th-grade Achieve3000 students over their non-Achieve3000 peers was 69 scale score points on the English II assessment. Based on these findings, it is recommended that teachers in schools that have Achieve3000 licenses actively encourage the completion of Achieve3000 exercises.