Comparative education scholars are often sceptical of teaching effectiveness research that compares 'teaching quality' using systematic classroom observation systems across nations. This study investigates how three international observation systems designed for comparative use and studies that apply them attend to three concerns intrinsic to academic comparative education field-conceptualisation 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, national) in contextualising their studies, and context is seldom used to interpret the results of teaching quality. All the studies suggest that their implications for research, policy, and practice, especially for policy, are vague. The study concludes with a discussion of how classroom observation research can build on both teaching effectiveness and comparative education perspectives.