As I recall, it was in the wake of the Boer War that the nutritional status of poor children became an issue. The army, it appeared, was no longer getting soldiers fed up on the roast beef of Old England, but stunted, rickety lads with bad chests. What to do? @ATMcCall says

that this was the point at which (in Scotland, at least) school dinners were introduced while, at the same time, the academic content of working class children's education was reduced, to make room for cookery for the girls and physical exercise for the boys. The idea was

that they could teach girls to produce cheap nutritious meals for their children, and raise a healthier generation. Because the high rate of malnutrition amongst Boer War soldiers was not the fault of the poverty of their upbringing, but their mothers' inability to cook.

Although there had been a gender divide in state education prior to this, the Boer War was the point at which it widened and calcified. It also made social mobility even more difficult, especially for girls. (Thank you, @ATMcCall )

In WWI, the poet Isaac Rosenberg, among others, enlisted so that his mother could get his salary. He was sent to one of the Bantam Battalions created for the stunted and malnourished children of the poor. If you're a bantam, that means you're cocky and belligerent, right?

It was from the experience of needing a well-nourished soldiery that free school meals and free school milk originated. It's telling that in the age of nuclear weapons, drones, and cyber warfare, it no longer matters.