Sorry I only have a moment Potato. At age 10, Dd is on track to do an IGCSE maths next year, she might also take geography, we will see how she manages. It is unlikely they will go onto further education in the UK, so it is likely they will take SAT's instead for American college entry.
With the caveat that I am only speaking with regards to my children and our experiences within the British state school system, and I am not making sweeping judgements regarding other peoples choices, I am happy to discuss conventional schooling. My youngest has never been to school outside of the house, but dd did complete 3 years - preschool, year one and most of year 2. She was ignored by the teachers, consistently. I dont have much time right now, but suffice to say the education she received or lack thereof at school was appalling. Anything she did learn, she learnt at home with me at weekends. She was bullied, left out and just not one of the popular children. As she said, in her own words, she was "not one of the golden girls, so noone ever bothered with her at school". She is doing wonderfully now, and has some lovely friends. Ds, who has always been homeschooled - and Im SURE Im going to be accused of boasting now, is just 6, reading chapter books, has started the first Galore Park junior math book and is flying through it, knows all his times tables, and not just in order, and is a great little footballer. It took at least a year to get dd to the point where she was fulfilling her potential, and I find that lost and wasted time, an absolute crying shame.