Participation in the School Breakfast Program is much less common than participation in the National School Lunch Program, even among children with access to both programs. This report examines the determinants of participation in the School Breakfast Program among third grade public school students, as well as the impacts of the program on food insecurity and children‘s risk of skipping breakfast. Data are from the Early Childhood Longitudinal Survey— Kindergarten Cohort and from the Wisconsin Schools Food Security Survey. The study found that students are more likely to participate when breakfast is served in the classroom, when time available for breakfast in school is longer, and when they come from lower income or time-constrained households. Children with access to the School Breakfast Program are more likely to eat breakfast in the morning and that program access may enhance food security among families at the margin of food insecurity.