From the abstract: "Despite the millions of dollars awarded annually by the United States Department of Education to build implementation capacity through technical assistance (TA), data on TA effectiveness are severely lacking. Foundational to the operationalization and consistent research on TA effectiveness is the development and use of standardized TA core competencies, practices, and structures. Despite advances toward a consistent definition of TA, a gap still exists in understanding how these competencies are used within an operationalized set of TA practices to produce targeted outcomes at both individual and organizational levels to facilitate implementation of evidence-based practices. The current article describes key insights derived from the evaluation of an operationalized set of TA practices used by a nationally funded TA center, the State Implementation & Scaling Up of Evidence Based Practices (SISEP) Center. The TA provided by the Center supports the uptake of evidence-based practices in K-12 education for students with disabilities. Lessons learned include: (1) the need to understand the complexities and dependencies of operationalizing TA both longitudinally and at multiple levels of the system (state, regional, local); (2) the relative importance of building general and innovation-specific capacity for implementation success; (3) the value of using a co-design and participatory approach for effective TA delivery; (4) the need to develop TA providers’ educational and implementation fluency across areas and levels of the system receiving TA; and (5) the need to ensure coordination and alignment of TA providers from different centers. Gaining an understanding into optimal TA practices will not only provide clarity of definition fundamental to TA research, but it will also inform the conceptual framing and practice of TA."