I was eating school dinners every school day during the same years as you, Badhorsey, (and several years either side as well), when I was teaching in a Sheffield secondary school. (I got a free lunch every day in return for being on call as the teacher in charge of first aid). My experience was very different from yours, as the food that was served in the school that I taught in was generally delicious (and with a good choice available). My favourite was individual pizzas, with loads and loads of cheese, served on a wholemeal base. They were lovely!
During my own school days, I went home for lunch in the primary years but had school dinners when I went to secondary school. I was dreading them but they introduced me to spicy foods (instead of the bland traditional 'meat and two veg' dishes that my mother had always served to me), with the excellent curries being great favourites of mine.