Between 2012 and 2018, the U.S. Department of Education invested nearly $350 million in 22 Comprehensive Technical Assistance (TA) Centers that operated across the nation. These Centers were charged with delivering TA that builds the capacity of state education agencies (SEAs) to support local education agencies in improving student outcomes. Centers were given broad discretion in interpreting and enacting this mandate. This evaluation sought to address the open questions about how the Centers designed and implemented the TA, what challenges they encountered, and what outcomes they achieved. With thorough documentation of how this process played out, stakeholders will be in a better position to inform future program improvement. Key takeaways from the study include: (1) Overall, Centers and their TA recipients reported that the Centers' TA improved the capacity of SEAs to meet their goals; (2) Centers shared similar approaches to the design and implementation of their TA. Those Center practices perceived to be instrumental to building capacity included: engaging a broad array of stakeholders to provide input on policy; providing products and tools for SEA staff to use as they took greater ownership of policy design and implementation; imparting organizational practices and structures resilient to SEA turnover and policy shifts; and flexibly adapting TA in response to changing priorities and needs; and (3) Centers and their TA recipients pointed to a few areas for program improvement, including clarification of the Centers' role and expected outcomes related to their work with LEAs, and further guidance for SEAs about how best to use the Centers. [For the final report, see ED599103. For the appendices, see ED599104.]