Purpose: This article gives an overview of the successes and lessons learned to date of the Education Endowment Foundation (EEF), one of the leading organizations of the What Works movement. Design/Approach/Methods: Starting with its history, this article covers salient components of the EEF's unique journey including lessons learned and challenges in evidence generation. Findings: The EEF has demonstrated that it is feasible to rapidly expand the use of school-based randomized controlled trials (RCTs) in a country context, set high standards for research independence, transparency, and design, and generate new evidence on what works. Challenges include the need to consider alternative designs to RCTs to answer a range of practice-relevant questions, how to best test interventions at scale, and how study findings are reported and interpreted. Originality/Value: This article addresses some of the key components required for the success of What Works organizations globally.