I'm on the fence regarding "good" food.
I say that as a trained cordon bleu Cook and a person who has always eaten well from childhood to adulthood.
At primary, private, school lunches were great.
At grammar school state, 1971, typical school lunches were:
Beef cobbler with vegetables and mashed potato
Liver and bacon with vegetable and mashed potato
Egg salad, an egg and a bit of grated cheese accompanied by a lettuce leaf on which there was a slice of tomato, a slice of cucumber and half a dozen pieces of cress with mashed potato
A roast - meat of some description, roast potatoes, veg and gravy
Fish (grey) in slimy and thin parsley sauce, mash and peas
Puddings were - puddings, stodgy, jam covered, fruit crumbles, dead fly pie, etc with custard or ice cream.
Sounds great doesn't it but if I describe the beef cobbler for example: gristly, grey meat swimming in watery gravy with globules of fat and a bit of disintegrating swede or turnip, topped with rock hard orange scone, watery cabbage and mashed potato, lumpy with black eyes, you get the message. Other meals could be similarly described. There were occasional things that were OK, for example: cheese, egg and bacon pie but not often.
Custards were processed and often coloured brown or pink, ice-cream was the cheapest available, crumbles were welded.
It was more or less inedible and aged 11, 12, 13 I recall being so hungry in the afternoons, stinging still from the lectures about the starving in India.
Frankly, chips and nuggets would have at least been edible and would have filled me up for the afternoon. I don't think I ever saw a piece of freah fruit being available or a vegetable other than Carrots, cabbage and peas.
Thankfully at third form, due to pressure from parents, we were allowed to take a packed lunch and mealtimes improved. I had a flask of soup or hot chocolate, a cheese or ham sandwich and an apple or an orange packed by my mother.
If school food is to be good, then the budgets need to be adequate - it costs.
Regarding dental health, genetically my first teeth were not good, some people's aren't. Look at the late Queen Mother and she was hardly deprived. DD's baby teeth were shocking - she had to have four molars extracted, aged 4. Not due to diet but because I had pleurisy at about 18 weeks pregnant and had to have strong, intravenous anti-biotics. It coincided with the development of the second molars.
Also loving all the suggestions for porridge. I expect those suggesting it imagine it made carefully for four servings with a little milk and water, gold top for the top, some quality cherries or berries and a little honey. It won't be. It will be like gloop or thick and lumpy with a bit of cheap processed syrup if the children are lucky. In the workhouse it was called gruel.