Outraged parents in Salt Lake City said the students at Uintah Elementary primary school had been humiliated.
The school system has launched an inquiry into the Tuesday incident, blamed on a sole "nutrition manager".
The children whose meals were put in the rubbish were given fruit and milk.
"I get that the school needs to be paid," said Senator Todd Weiler. "But this was bullying."
Life is like a penny, you can spend it on what you like, but you can ONLY spend it once.