Jack...they can't.
When its time for kids to start of their GCSE options, than I can't see any alternative to a proper school, unless you have the odd science Lab hanging around the house.
I could probably teach a young child to read and write but having no teaching other training or other skills, I wouldn't be able to go much further.
I am loath to add this, as I have had enough opprobrium heaped upon for one day, but I agree about the interaction with other kids, as well as the general social skills that everybody needs as we grow up.
My, admittedly, limited experience with home schooling is that it is almost always due to religious reasons, rather than an attempt at a more rounded education.