DS attends part-time (age 6) but - the important bit - for the rest of the time he has 'Education Otherwise than at School' - which in his case is an ABA programme. So he still receives full-time education but not all of it at school - you can get Education Otherwise on grounds needs cannot be met fully or partly in school. His Statement is for Ed O/wise with part-time attendance at school. See Education Act 1996 for info on Ed O/wise
DS could attend fulltime, its just the staff don't know how to teach him so there would be no benefit - he learns more in ABA 1:1 than he would going to school more. He would learn less if he went more.
All children are entitled to fulltime education unless they have medical (not behavioural / SEN) needs. DFE guidance and an Local Govt Ombudsman Report 'Out of School Out of Mind' both confirm this. Education Act 2010 extended the right to fulltime school to children in PRU's as well. Guidance also says child should receive as much education as possible not just 5 hour minimum
If a school says a child can only attend part-time due to SEN then it is for the LA to provide a FT education either via home tuition, PRU, putting more support into school so child can spend half day in 1:1, dual placement etc etc. The starting point is not to only offer part-time education.
If schools / LA only provide part-time then that is an unofficial exclusion & discrimination.
Parents can request flexi schooling, but schools cannot impose flexi schooling on parents!
If behaviour is bad enough to merit part-time attendance then the LA should usually be placing the child temporarily or permanently in a different school - usually specialist unit etc.
Badger you should send this to the head of SEN at the Council and ask for their views - possibly do this via a parent group / local sen charity?
Is your school an academy?