The school should not be doing this. You would be well within your rights to refuse to collect early unless the school is formally suspending DS.
It may help you to read the government suspension and exclusion guidance if you haven’t already, and remind the school of it. You can see it here. In particular:
“Telling or forcing a pupil to leave school, or not allowing them to attend school, is a suspension (if temporary) or permanent exclusion (if permanent). Whenever a pupil is made to leave school, or forbidden from attending school, on disciplinary grounds, this must be done in accordance with the School Discipline (Pupil Exclusions and Reviews) (England) Regulations 2012 and with regard to relevant parts of this guidance.
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, or for a reason such as, academic attainment/ability; or the failure of a pupil to meet specific conditions before they are reinstated, such as to attend a reintegration meeting.
21.If any of these unlawful exclusions are carried out and lead to the deletion of a pupil’s name from the register, this is known as ‘off-rolling’. Further examples of off-rolling include:
•exercising undue influence over a parent to remove their child from the school under the threat of a permanent exclusion and encouraging them to choose Elective Home Education or another school place
•moving a pupil to off-site AP where that is not in the best interests of that pupil
•encouraging a post-16 student not to continue with their course of study when this is against the best interests of that pupil
•sending a pupil home without a formal suspension regardless of whether it occurs with the agreement of parents
•placing a pupil on a part-time timetable for behavioural reasons
•Intentionally removing a pupil from the school roll without correctly following regulations”
Don’t worry if they go on to suspend. 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) means DS would be eligible for alternative provision once he has reached that threshold.
Whatever you do, put it in writing so you have a paper trail as evidence.
Where are you in the EHCP process? Is the LA sticking to the timescales?