Recent studies have suggested that quality of delivery matters to achieve better student outcomes in the context of school interventions. However, studies rarely measure quality of delivery and test its association with students' outcomes, perhaps due to lack of clarity regarding how to measure it. Here, we offer recommendations on how to select or design measures of quality of delivery. These recommendations focus on identifying teaching practices that help students to develop proximal outcomes during the delivery of an intervention. Additionally, we illustrate an application of these recommendations to the study of quality of delivery in a cluster-randomized efficacy study of Brainology, a program that promotes students' motivation and learning. We found that, although teachers fluctuated in their quality of delivery across lessons, students who received the intervention with higher quality of delivery on average increased more in targeted proximal outcomes (effort beliefs and learning goals) than students exposed to low quality. We discuss these results in terms of their implications for measuring quality of delivery, supporting teachers, and studying the conditions that make school interventions successful.