Here's a topic that's come up elsewhere; I've heard some interesting ideas and think that a combination of them is probably right, but I'd be interested in hearing opinions.
What do Wizard children do for "school" up to age 11 and admission to Hogwarts? I'd guess a mix of things.
Obviously, Muggle-borns (and Muggle-raised, like Harry) who know nothing about the Wizarding world until The Letter comes would go to regular Muggle schools. Did you ever wonder about Hermione's pre-Hogwarts days? Did she ever do "weird" things that her parents/teachers couldn't explain? (As when Harry makes his hair grow out, frees the snake at the zoo, etc.)
I think, however, there must be Wizarding grammar schools, at least in the larger metropolitan areas, where there would be some concentration of magic folk. London would certainly have something, and I could also see some historic, exclusive school specifically for the children of the ancient, pure-blood families (the Malfoys and their ilk). I've had a thought, and will probably use it, that Prof. McGonagall is headmistress of a good Wizarding grammar school in Scotland before she comes to Hogwarts. For Wizarding families who don't live in highly populated areas, there's probably a lot of home schooling (I'd expect this of the Weasleys), or the parents could hire a tutor for the kids, if they can afford it.