Can I refuse my son taking his GCSE

Hi All,

Struggling to start here and unsure how to begin so if this seems a bit jumbled and thrown together, please excuse me. 

My son has been struggling massively at school for years now, my wife and myself were convinced he had some type of learning disability and have been arguing with his school for years. today things finally came to a head, myself and my wife arranged for a meeting at the school after receiving his mock exam grade. All of which were grades g and u. For the first time today the school actually took seriously what we were saying after we in no uncertain terms made our anger and frustrations about not being listened to clear. The SEN teacher who has been assessing our son and was adamant he was just a lazy, moody teenager completely dissmissed the idea that there was anything underlying, although did point out that as he seemed to be a day dreamer he may have petit mal epilepsy and suggested we should visit the Dr just to rule this out. less than 2 minutes sat in the Drs office and that was dismissed immediately and we were informed that she believed our son may be Autistic. I am unbelievably angry that it has taken so long for this to be picked up. Autism is not something that we are to familiar with but it was something we asked the school to asses him for and we're told it was a definet no and there was no  point. it is now less than 4 months till his GCSE exams, and he is clearly going to fail them and i believe he has been massively failed by his school. At this moment my way of thinking is why should we put him through the stress of these exams only for him to try his hardest and take another un necessary knock to his confidence. His predicted grades u, f, E. Is anyone aware if it is legal to stop my son sitting his exams. I am not talking about pulling him from education altogether and we already had plans in place for him to go to college next year to complete his Key skills maths and English. Any advice anyone could give would be greatly appreciated. 

Thanks

Scotty