I have a Aspie son (learns at home). As Sarah mentioned we did something similar in giving him an old pc that he can re programme etc as much as he likes. With the proviso that he never does anything like that on the family pc (which is now set up so that important stuff can only be done from my windows). Of course he is older than your ds
Could you and/or the school provide him with a laptop to use in class?
Not only would he not likely be interested in doing things on the school computer but he'd still be getting IT use and possibly help him stay on task for work given to him in other areas (don't know if he has those sort of problems but mine did and working on pc helped enormously).
The laptop could be configured to ensure he can't access into areas he shouldn't
What written work he does could be printed out at the end of each class or day or whatever.
I don't live in UK so wouldn't know names of any organisations that would do this but maybe there are some charities etc that provide free/cheap reconditioned laptops? Would somewhere like the NAS (or similar) know of such a thing maybe?
I agree that SN kids need to learn to control what they can where that is possible however something like this is not necessarily within his control. Sometimes it's easier and kinder for them to have an alternative rather than feel negative about how they (naturally) are, hence my suggesting a laptop in class. Just don't see the need for you, him and the teacher to be banging your heads against the proverbial wall when it might not be necessary
Also given his young age maybe you could try some re enforcement techniques (e.g. small reward for every five minutes he leaves the pc alone, time span gradually increased). However in a busy classroom I can't see how a teacher would have time to do that.
Something I used with good success with my dd was to make up little books/stories that she would either have with her for a particular event or be hung up in a place where that activity would be done. Mine were just made from folded bits of paper glued together with pictures as well as a few words on each page describing each step
- You have a particular goal you want your child to work towards so you make a book of each step the child needs to take to achieve that aim (keep it short and simple). You ensure the child constantly reads that book when appropriate, following one step at a time re enforcing how to achieve said goal. Again don't know how successful this would be with your son - don't know how high or low on the scale he is or whether the teacher would have time to re enforce this with him, which leads me back to him using a laptop to draw his attention away from the school pc.
Even though Aspies have to deal with similar things, each child/adult has them at varying levels so what works for one doesn't necessarily work for the next.
Of course as you say if the school had a password on the pc it could only be accessed when allowed
Wish I could be of more help.
Be interested to hear about what does or doesn't work, am constantly re evaluating how I do things with my three.
Good Luck