My younger sister "works" in a public school and claims that most of lunches served go in the trash, and my mother believes the claim.
A quick search shows that a significant amount does indeed. But at 40% +/-13%, saying "most" seems a stretch.
"A 2019 study of school cafeteria food waste found that 27% to 53% of the food served in an American school cafeteria was thrown away. These results are similar to other studies of American cafeteria food waste. Among other nations in the study, so-called plate waste accounted for 23% of total food served in Sweden, 20% to 29% in Italy, and 30% in Spain."
https://thenevadaindependent.com/fact-briefs/does-a-significant-percentage-of-free-school-meals-wind-up-in-the-trash