Understanding experimental design (e.g. control of variable strategy or CVS) is foundational for scientific reasoning. Previous research has demonstrated that demonstrations with cognitive conflict (e.g. asking students to evaluate and explain different experimental designs) are effective in promoting children's scientific reasoning, however, the implementation of this approach often requires significant instructional time and resources. This study reports the impact of a brief, scalable intervention on one component of scientific reasoning, understanding experimental design, by providing brief instruction on the control-of-variable strategy (CVS), embedded in a food science activity (popping popcorn). Three-hundred and seven (307) 3rd-5th graders in the midwestern US participated in either a CVS intervention or a demonstration on the science of popcorn without a CVS intervention. Performance on a pre-activity test (involving identification of good and bad experiments) did not differ between conditions. By contrast, post-activity performance was significantly greater for classes who received the CVS intervention. Thus, a brief discussion of the CVS embedded within a food-science demonstration can have a meaningful impact on children's understanding of conducting a quality experiment. Our results demonstrate the efficacy of a simple, low-cost intervention for CVS that is potentially scalable.