It never dawned on me as a child, but a couple things jump out at me now as to what I was fed in elementary school.
1. Your drink choice was milk or chocolate milk. Both had artificial sweeteners. Apparently, we had no lactose intolerant kids in the whole school.
2. We were fed lots of bread and potatoes. Even the main dish was often pizza or similar, which contains bread.
3. Green vegetables were exceedingly rare.
4. A kid in Kindergarten and a 6th grader got the same lunch.
In retrospect my lunch diet was atrocious due to this as a kid. You don't need to feed kids sweetened crap all the time. It's especially hard to justify given that all the public schools had complete kitchens that were used every day.
Basically, public school was just state sponsored day care where I grew up. Not only that, it was awful quality day care.