In one of my worlds, wizards are so distrustful of each other and so paranoid about people stealing their power, it's all home-schooling with a high rate of fatalities.
When a wizard is ready to start a family, he finds a homely, unloved, sickly, poor girl who's willing to serve him for twenty years in exchange for a better life. (The ancient texts prescribe picking the most wretched young woman available.) They go to his isolated home, he makes her healthy and beautiful, and they begin making babies.
Each child is raised until they're about three years old, then the wizard puts them in a moon bath, effectively freezing them in a moment in time. They do that again, and again . . .. It's common to accumulate six before continuing, but many wizards feel more comfortable with eight.
All the children are then all raised together. The mother teaches them reading, writing, music, etc.. The father teaches them the ancient tongue and charms appropriate for their age.
By the time one of them starts puberty, there's usually only three or four left because any signs of disloyalty towards the father is fatal, very messily fatal in front of the other children.
The moon bath is employed again so each child is raised separately while they go through the major stages of puberty. No magic is taught/done then because it's too dangerous.
When they're all ready again, the wizard begins teaching them the usual range of spells, enchantments, and incantations. By the time they're about twenty, there's usually only one or two left. (If there are more, the slower ones are culled.) Each is given a part of the house in which to live. There they practice their arts and further educate themselves, able to consult their father and their father's library but mostly staying in isolation.
When they feel they're ready, they leave home, never to return. With the children gone, the mother is once more made young, healthy, and beautiful, given a reasonable fortune, and goes to seek her own way in the world. The only constraint on her is that she must keep alive the lie a woman serves a wizard for twenty years when in reality it's at least sixty and may be eighty years.