Hi there, I appreciate that you posted this last year but incase anyone stumbles upon this thread in a similar predicament -
my son has been diagnosed with autism after being unable to focus and having behavioural issues at his primary school.

Now he attends Royal School Manchester: https://www.seashelltrust.org.uk/our-school/ (not sure where you're based OP, sorry if this is too far away!) which is part of Seashell Trust. He's really come on since being there for the last year, their sensory facilities in particular are amazing.

Hope your grandson is doing okay and also his daddy :)