We had a school once. You know where, Starlight
and instead of educating my children - who had statements and full time 1:1! they put them in the office to be babysat by the office staff and used their LSAs for general assistants.
only found that out when one TA risked her job and showed up at our house one night, in tears.
We left the area shortly after. Just phoned the school and said they aren't coming back.
That was the most extreme, there's been not so good provision, and examples of their entire education being the responsibility of the TA because the class teacher has basically opted out. 
Where they are now is very good. in fact, they've been consulting with outreach to come up with an individually tailored timetable for my youngest, who has been so stressed that he became very ill and very violent. it's got physical activities and 1:1 sessions and down time built in.
This happened after we got cross because it felt like they weren't appropriately differentiating the curriculum for them, and that our youngest wasn't coping. The ed psyc got involved at that point.
They've both got and always have had full time 1:1, but that isn't in itself a guarantee of anything, as we found out!
It is unacceptable for your son to be wandering about. The school has a duty of care and they, frankly, need a rocket up the arse.
What outside agency involvement do you have? I found that the more outside people were going in and asking the schools to show what they were doing, the more the schools put things in place! funny that... 