Why are adults charged more for their school lunches when they are getting the exact same tray as a student?

That is a policy established by the Indiana Department of Education Child Nutrition Program. The policy states in part, "Meals served to adults are neither eligible for federal or state reimbursement, nor do they earn donated food assistance for the School Food Authority." In other words, the meals of school children are subsidized by both State and Federal entities, adults are required to pay the full and actual cost of the meal.