This meta-analysis examined learners' academic achievement in Universal Design for Learning (UDL) environments compared to business-as-usual conditions. Twenty studies, consisting of 50 individual effects, met the eligibility criteria, focusing uniquely on participants' learning and treatment/control designs. Academic achievement was analyzed for pre-kindergarten to adult participants. Results yielded a moderate positive combined effect for learners receiving UDL treatments (g 1/4 0.43), indicating mod-erate efficacy of the UDL-based instruction. Five significant moderators were identified. In addition, the UDL Reporting Criteria were employed to assess whether studies included information regarding UDL-based design components. UDL's emergence as a research-based practice for diverse learners is discussed. (c) 2022 Elsevier Ltd. All rights reserved.