Numerous reviews have synthesized the empirical research on the effectiveness of teacher education, highlighting teacher education effectiveness research (TEER) as an emerging research paradigm. Our systematic search identified 27 reviews related to TEER, wherein teacher education is broadly understood as comprising all stages of teacher professionalization--namely, initial teacher education, teacher induction, and teacher professional development. In reviewing these reviews, we carry out a synthesis of existing research on TEER. Guided by four research questions (RQ), we focused major frameworks (RQ1), outcome measures (RQ2), processes (RQ3), and central research gaps (RQ4). Highlights: Only few reviews provide a background or macro framing, whereas most reviews apply TEER for examining a specific topic (RQ1); outcome measures often relate to the notion of teacher competence, making increased competence the true outcome of TEER (RQ2); coursework is the most dominant category of characteristics-forming processes (RQ3); the frameworks underlying the outcome measures appear to be an object of criticism on a theoretical but even more on a methodological level. Building on these findings, we suggest a processes-and-criteria classification (PCC) grounded in basic distinctions of the various studies synthesized by the reviews. We discuss perspectives on how this classification may provide an orientation for future TEER studies.