To answer that, let me present two models of social development.
Children are gathered into small groups, their age and home address the primary selection criteria. Outside of a few exceptions, the children have no say in the group they are chosen to be in. The group will be required to gather in the same room, or small selection of rooms, at the same time every weekday.
The group will be allowed outside the room they’re in, but only at set times. During those times they will be encouraged to expend their physical energy as much as possible to ensure focus for their next inside session, and will also be allowed to eat.
Back in the room, the group will be asked to switch between independent and collaborative work. They will be measured and marked against a set of over-arching standards. Most will know how their marks compare to the others around them.
A small group of adults will be spread throughout the rooms, and will be responsible for the meeting of standards and the following of schedules and rules (whether they agree with them or not). If a child can’t meet the standards over a period of time or breaks the rules of the group (for example, chooses to continue with outside time when the schedule states it is inside time), behavioural correction will be applied.
The other children in the group, generally, will know when and why this has occurred, and for who.
Provided they don’t move homes, this small group will spend many years together.
Children split their time between being at home and being out in the world, interacting with all the different people where, when and why you would naturally expect them to along the way.
There would be few home educating families that aren’t continually asked how their children will develop the social skills they’ll need for entering the ‘real world’.
The answer, really, is quite simple: they never actually leave it.