When DS was 8, we asked our then headmaster if he could link us into a school on the other side of the world where he had worked a few years back, so DS wasn't missing out. (DH had had a desperate illness, and with regained health wanted to see New Zealand).
To his eternal credit, he said... FFS, take this very precious window of health and money to travel. Read books together, teach child to read airline timetables for maths, and look at what's around to teach the rudiments of physics and chemistry and history, geography, RE and geology... whatever is interesting wherever you are. DS slotted right back in to his class six months later, without a blip. We read, we wrote, we took every chance we got to put him in school for a few days wherever we went. Education, before A level study, is just stuff most people should know. GCSE is a minimum level of competence. Non mainstream school is just fine.
A friend says teach them to read, write, arithmetic including tables, and to swim, and drive, and cook, and they can make sensible choices.