Is there any reason he isn't on SA Corny?
If he has a dx and the school is aware, he should be on SA, which would identify him to his teachers as a child who needs either help or allowances in certain areas.
Being on SA would mean the school would help come up with strategies to help him remember things and manage his organisational skills better, it could also mean allowing him to leave the previous lesson a couple of minutes earlier than his classmates, to afford him enough time to get change for PE.
If the SENCO has been made aware of his dx and you have given her the necessary info to understand his difficulties, she should have put him on SA and I would follow that up.
When was the last time you had any Occupational Therapy input? It might be worth contacting them. Ds2 has hypermobility syndrome and doesn't qualify for any actual 'therapy' from OT, but they have just spent an hour talking to him about what he struggles with and what he feels might help him cope with school a little better, followed by trying out some different pens, pencils, scissors etc. They then went into school, met with the SENCO and gave them lots of information on how he should be being supported, as well as arranging for a specialist PE teacher to go in and 'teach' them how to differentiate for him sports lessons. Google your local OT department and give them a call, as referrals differ from area to area, but in our area, when a child has been seen once you can then self refer back for help with specific issues whenever you like.