I hated school, I just wanted to go and do my own thing learning/listening to music etc. Now I look back I am glad I was not home schooled as I would have missed out on so much personal development that I needed.

I learned how to become a member of a group and move between social groups.
I had inspirational teachers that I learned from.
I had scary teachers that I learned from.
I learned boundaries and the rules in life to get you by socially.
I had my first girlfriend when I was thirteen. I was quite shy and it only happened because we were in same room all day.
I learned to become a judge of character rather than a judge of what someone has materially.
I made lifelong friends that I still have to this day.
We formed a band.

The list could go on and on.

I think school gives you priceless life lessons you can't get sitting on your own in the house and I think your lad knows that. He sounds like he is easily clever enough to get his GCSE's and go to school as well like most normal people do. I use the words most and normal because when you don't fit in with what most people do you can be singled out, which is just another life obstacle.

It's also about feeling accepted by your peers, being able to compete and grow with them too. For instance, you can't play kick about in the yard on a morning with your mates, you can't go on a school trip either if your at home. There is so much he will be denied in life by not going to a school.