Out-of-school time (OST) programs serve youth from diverse demographic backgrounds. OST programs, whose informal settings provide opportunities for experiential learning, can address this problem by implementing nutrition and food-preparation programming to improve participants' dietary knowledge and behaviors. In this article, the authors describe WeCook: Fun with Food and Fitness, an OST curriculum for fourth- and fifth-grade students focusing on food preparation, nutrition, and physical activity. In the process of piloting this program, they discovered the need for a nutrition assessment that would be time-efficient, developmentally appropriate, and user-friendly. Their solution was to develop a novel tool called the Healthy Plate Photo (HPP) method, based on the U.S. Department of Agriculture (USDA) MyPlate guidelines (USDA, 2017). They used this tool, in conjunction with a conventional paper survey, to assess nutrition knowledge before and after children participated in WeCook. HPP's innovative approach is appropriate in OST settings because it is hands-on and fun for students; it is also easy for staff to conduct. To demonstrate their nutrition knowledge, children build a healthy plate (as defined by USDA) using plastic food models. The results of the authors' pilot study suggest that the HPP method can be a practical and useful nutrition assessment tool for OST programs to use with youth from varied socioeconomic and racial/ethnic backgrounds.