Opportunity to learn (OTL) is a ubiquitous measure of the likelihood of learning in educational research, which typically has been characterized by three dimensions: time, coverage of content, and quality of instruction. The last dimension has been defined in highly divergent ways, which gives it a double-edged nature. While it may be operationalized to better serve a specific problem or context, it also makes it harder to achieve consensus or derive broader implications across studies. Using the four design principles from the Productive Disciplinary Engagement (PDE) framework, we show how PDE can characterize the quality of instruction dimension in OTL that reflects contemporary understandings of the end-goals of science education i.e. learning science as practice. This revision is valuable for science educators and evaluators who rely on OTL measures for it helps them: i) evaluate the quality of instruction consistent with reformed science teaching in valid and reliable ways, and ii) address questions about the adequacy of content coverage in the subject. We exemplify analysis using this refined OTL model with a case study of middle-school learners in Singapore engaged in the challenging scientific practice of argumentation.