If you want DS to attend school full-time, he can unless the school is formally suspending DS. Inform the HT in writing that DS will be attending school full-time after Christmas unless they formally suspend. You don’t have to allow the school to continue to unlawfully informally exclude DS.
Don’t worry if the school suspends. A formal suspension rather than an unlawful informal exclusion it will a) provide you with evidence of unmet needs, b) force the school to follow due process, c) limit the number of days the school can suspend for, d) allow you to challenge any suspension, and e) once DS is compulsory school age will ensure he receives alternative provision once he has reached that threshold.
2.17 of the School Admissions Code (which you can see here) makes it clear it is the parents’ choice:
“Admission authorities must provide for the admission of all children in the September following their fourth birthday. The authority must make it clear in their arrangements that where they have offered a child a place at a school:
a) that child is entitled to a full-time place in the September following their fourth birthday;
b) the child’s parents can defer the date their child is admitted to the school until later in the school year but not beyond the point at which they reach compulsory school age and not beyond the beginning of the final term of the school year for which it was made; and
c) where the parents wish, children may attend part-time until later in the school year but not beyond the point at which they reach compulsory school age.”
If you haven’t already read the suspension and exclusion guidance helpful here. Most of it applies to those below compulsory school aged. Where it doesn’t, it explicitly says so as stated on page 6.
Some bits you particularly might find helpful are:
“19. Suspending a pupil for a short period of time, such as half a day, is permissible but the formal suspension process must still be followed. Each disciplinary suspension and permanent exclusion must be confirmed to the parents in writing with notice of the reasons for the suspension or permanent exclusion.
20. Any exclusion of a pupil, even for short periods, must be formally recorded. It would also be unlawful to exclude a pupil simply because they have SEN or a disability that the school feels it is unable to meet…An informal or unofficial exclusion, such as sending a pupil home ‘to cool off’, is unlawful when it does not follow the formal school exclusion process and regardless of whether it occurs with the agreement of parents.”
And
“30. A part-time timetable should not be used to manage a pupil’s behaviour”
As part of the next AR I would look to improve section F. Both for the SALT provision and OT (the school may be implementing what is already in F, but F needs improving to include direct OT provision and indirect OT provision for things like time allocated for the OT to write updated advice and information prior to ARs, attend ARs, train school staff, liaise with other professionals involved, etc.) If the LA won’t make the necessary amendments, you will get the right of appeal following the next AR.