Modifying the school food environment is on the national agenda as one strategy to improve the nutritional quality of children’s diets. Because few environmental-level interventions have been rigorously evaluated, the evidence base to inform programs and policies is limited. Of concern is the impact that changes to cafeteria offerings will have on participation in school meal programs. This study evaluates school lunch participation in the setting of a year-long middle school cafeteria intervention by examining the association between body mass index (BMI), sociodemographics, and the purchases of school lunch meals. IMOVE meals were healthier choices that met stringent nutritional criteria and were offered alongside standard lunch meals. Students who were overweight had a significantly higher purchase rate for both types of meals compared to those with a healthy BMI. Non-white race, younger age, being male, and low-income status were also significantly associated with participation in school lunch. Results indicate that nutritionally vulnerable students participate in school lunch and are equally likely to buy healthy alternatives or standard meals. This behavioral observation has important implications for school foodservice programs and policies. These results are timely given recent federal legislation to improve the school food environment to influence students’ food choice behaviors.