“Attendance [at magic school] is now compulsory for every young witch and wizard,” he replied. “That was announced yesterday. It’s a change, because it was never obligatory before. Of course, nearly every witch and wizard in Britain has been educated at Hogwarts, but their parents had the right to teach them at home or send them abroad if they preferred. This way, Voldemort will have the whole Wizarding population under his eye from a young age.”
— from “Harry Potter and the Deathly Hallows” by J.K. Rowling