Gcse meltdown, what do we do now? Please advise

Hello, I have never posted on a forum before, but I am unsure about what to do next. My son is 15 and in year 11, he was diagnosed with Aspergers and anxiety in year 7, he has always been in mainstream education. He has mostly coped, his strategy is to be the invisible boy at school and would rather die than break a school rule. He has reserved his meltdowns for home. He goes to the large comprehensive school closest to our home, so he has been around the same group of kids since nursery as we found change difficult for him.

Unfortunately  the 6th form of  our school is selective, all along I've been told don't worry he'll get in, including by the senco. He doesn't have a statement, but the school have provided a lunch club for sen kids and he has a small group of goodfriends from this. 

The problems began in February after his mock exams, his anxiety escalated and he stopped being able to go to school. He was referred to camhs and he is getting therapy and help from them. He did not return to school and so missed all the revision lessons. He has managed to go in for a few of his exams. The pressure of taking Gcse's and needing to get the right score just to stay in his school pushed him over the edge. I said he could go into the school's 5th form to retake if needed, but this leads to a complete meltdown.

He needs help with study techniques, life skills and communication.

He has a place at this 6th form and the other localcomprehensive school, but he didn't even take hisEnglish exam. Will he cope with 6th form if he gets in? Are there any special needs 6th forms, even private ones? Are there any summer schools to help with the transition process? I am looking into a learning difficulty assessment, but the senco has never heard of it! 

Advice please!