This report evaluates the effects of Lexia[TM] Core5[TM] Reading (Core5) -- a product of Lexia Learning Systems -- on the reading achievement of students in grades 3-5 during the 2021-2022 academic year. Core5 is a program that focuses on various student literacy skills, such as fluency, vocabulary, and comprehension. This report represents the first study in a broader effort to develop independent and rigorous research evidence about the effects of Core5 on student achievement. The authors compared the performance of students in a school district that used Core5 with similar students in similar schools across the United States that did not use Core5. The analyses estimated that students who used Core5 experienced larger reading achievement gains, on average, than their counterparts in the matched comparison group. Differences in outcomes measured in this study are likely to have been caused by Core5 use, but the methods used cannot unambiguously rule out selection bias to establish that causality. Moreover, study results might not generalize to all grades in which Core5 is offered or to all U.S. schools. [The research described in this report was sponsored by Lexia Learning Systems, LLC.]