Executive function (EF) measures used with African children heavily depend on task-based assessments normed in minority world settings. This reliance poses a challenge as it limits the understanding of how children display their EF behaviors within their own culture. Environmental factors including income and parenting are associated with children’s EF development. In addition, culture-specific practices may shape what EF behaviors are adaptive. Therefore, tasks that do not incorporate culture-specific indicators of EF may lead to misinterpretation or underestimation of children’s true EF capabilities in these settings. To bridge this gap, we used a qualitative approach to design a new observation scale for assessing EF in naturalistic classroom contexts. This paper describes the qualitative work leading to the design of the observation scale, which was later piloted in a quantitative study (reported elsewhere). To design the observation scale, we asked 16 preschool teachers in Nigeria to describe observable behavioral indicators of young children’s EFs based on their own classroom experiences. Their responses were thematically analyzed using a deductive approach, based on the EF constructs of inhibitory control, working memory, cognitive flexibility, and planning. We used the codes from the thematic analysis to develop a set of pilot items for an observation scale aimed at assessing EF in context. This set of items was shared with international experts on EF who provided feedback on the items’ face validity; a final set of items was extracted to constitute the new observational measure. Our findings suggest that using qualitative approaches can help inform the cultural relevance of instrument design. Theoretical and practical significance of the findings are discussed.