If things have become difficult since the beginning of the academic year, you need to know, apart from sending him home in the afternoon, what is happening to support him in modifying his behaviour in school. Does he have an IEP with targets that you can support at home? Is there a prospect of referring to an EP for additional targeted support?
It’s important to bear in mind that, in the past, schools could make a referral to EPS and had a certain number of visits per term from the EP allocated to the school. Schools could refer to the local Behaviour Support Team too. These days, with such tight budgets, those services are squeezed. It also depends on whether the school is LA or academy.
I would expect the school to be sharing targets with you and working on those, reviewing them and setting new ones if appropriate. After doing that, if there is little improvement, I would expect a referral to a outside agency and potentially moving towards an EHCP.
As far as the mornings only is concerned, it used to be the case that a part time timetable was possible in the short term, but that it should be part of a formal plan to reintegrate into school full time. I don’t know whether this still applies however.