The key to dealing with anxiety is to not back away from what makes him anxious. But simultaneously you need to be supportive, so any people around DS getting cross will make it worse as it will heighten the fight, flight or freeze response. Can you afford some private therapy? There is no point trying to access some from the NHS, he will be an adult before it comes through. Some CBT would probably be very helpful, but it needs to be someone who is experienced in his age group.
If you dont get on top of it now, it is highly likely to get worse as he gets older.
In the meantime
Name his anxiety and discuss the situations that set it off for him
Agree that these situations do make him anxious and this is not something that he can just turn off, and must be very annoying for him
Walk through how he physically feels when he gets anxious..heart racing, stomach upset, tears, clenched jaw, wants to run, wants to lash out…..tease out and focus on the physical sensations not the emotional ones (i dont want to go inside)
Write a list of his physical sensations and stick it on the fridge
Explain that these feeling are as a result of his body getting confused and making adrenalin accidentally. The adrenalin makes him have these physical changes and that it is what makes him feel the way he does.
Explain that the adrenalin only lasts for 10 mins or so, and that is why he is fine later on if he can stick it out. (As opposed to it being a actual problem in which case he would not enjoy any of school at all)
See if you can get him to agree to try an ‘exposure’. Agree a situation that normally makes him anxious. Hopefully one that you can artificially create (so starting the school day wont work) maybe being dropped off at a friends house..friend needs to be in on the plan
Head to the drop off point with a copy of the list of his symptoms.
Wait for the anxiousness to start and then gently ask him to check in with his body and notice which symptoms he is getting. Dont actually try and leave him, stay with him and help him name what is going on. Try and get him to persist in that state of being uncomfortable, coach him through it with lots of encouragement…get him to breath steadily, try to relax his muscles and be aware of what crazy symptoms his body is trying to bamboozle him with, time how long he persists. If he wants to stop and leave, let him. Write down his ‘exposure’ time . The next day, do it again and try and beat his last time. Keep going again and again. Eventually he will outlast the adrenalin and will be amazed that it calms down and he is still there, all in one piece with you right next to him.
That is the win. This technique, if it works for him, will probably need refreshing every couple of years, but he will be able to use for the rest of his life in similar situations. The aim is to coach him on how to control his reaction to his own adrenalin not deny it, or get him to hide from it.