Comparative education scholars are often sceptical of teaching effectiveness research that compares 'teaching quality' using systematic classroom observation systems across nations. This article investigates how three international observation systems designed for comparative use, and studies that apply them, attend to three concerns intrinsic to the field of academic comparative education--"conceptualisations of teaching quality," "attention to context," and "implications of results." The analysis indicates similar conceptualisations of teaching quality yet divergent assumptions about the teaching-learning relationship across systems, and little focus on the comparability-validity trade-offs. The studies had limited attention to levels of context (classroom, school, and national), and context is seldom used to interpret the results of teaching quality. The implications of all of the studies for research, policy, and practice, especially for policy, are vague. The article concludes with a discussion of how classroom observation research can build on both teaching effectiveness and comparative education perspectives.