I'm sorry, I don't have much experience (yet!), as my kids are younger, but am sympathetic and wanted to bump for you.
A friend of mine has a daughter who has struggled with Secondary for a variety of reasons. The school has been very good at working with the mum, child and teachers: what does your children's school say?
I was out of school for a year and then put in a pru but has not attended for 2 months. The other 2 have not been since the summer holidays last year. The school, camh's and the social worker are finally working together as I'm going around in circles. The school tried the reduced time table of 3 hours a day but some teachers were telling my son he had to leave after 2 hours because they couldn't handle him. They are in the process of applying for a ehcp for him and told me to look for another school