Regardless of what the main course was in a school meal, it came with a carton of milk, with some schools having a few other options as well. The reason dates back to the 1940s, after the Great Depression ended, and eventually led to a law in the United States.

The Great Depression left many men, women, and children malnourished, so offering meals at school was the solution to these vulnerabilities. Milk was included because it offers 13 essential nutrients, including protein, calcium, potassium, and vitamin D, meeting many nutritional requirements.

Schools can offer fat-free and low-fat milk, but not 2% or whole milk, and some districts even banned flavored milk for a while since it has more calories and fat. Schools must also include lactose-free milk options at the request of students with allergies.