Researchers and policymakers in the US and beyond increasingly seek to identify teaching qualities that are associated with academic achievement gains for K-12 students through effectiveness studies. Yet teaching quality varies with academic content and social contexts, involves multiple participants, and requires a range of skills, knowledge, and dispositions. In this essay, we address the inescapable tension between complexity and scale in research on teaching effectiveness. We provide five recommendations to study designers and analysts to manage this tension to enhance effectiveness research, drawing on our recent experiences as the first external analysts of the Measures of Effective Teaching (MET) study. Our recommendations address conceptual framing, the measurement of teaching (e.g., observation protocols, student surveys), sampling, classroom videoing, and the use and interpretation of value-added models.