Harry: He has been to muggle school. He was in a difficult family situation, but this is no excuse for not having friends. He was probably a shy boy, sitting in the back and making average results.
Hermione: She must have been in muggle school, too. It is very likely that already there she has been a "know-it-all." Maybe she had one or two bright friends, but I think it was a relief for her to change school, because her attitude creates frictions. In one word: she was a freak.
Ron: Where did he learn to read and write? Do wizards send their kids to muggle school? Do they teach themselves? Are there basic schools for wizards? The latter is unlikely, because from the travelling to the wizard championship we know, that very few wizard families live around the Weasley's home. So Ron probably didn't have friends of his age. Otherwise he would have known Luna better, who happens to live in the same area.
Especially Ron's early school career is very mysterious.
