I think you need to speak to your Local Education Authority to seek advice on this. If you look in the Yellow Pages you should also find a local Supportive Parents group in your area.
Are you going to be moving a long way away, and choosing a totally different school in 3 weeks' time? Schools have to take pupils whether they like it or not, but if the Head is that much of an idiot you probably wouldn't want Tom to go there anyway.
We've had a lot of problems with schooling, my son was excluded when he was 7. He has ADHD and has been badly bullied, but they decided it would be easier to get rid of him than trying to help him. We researched all the facts and attended the appeal panel armed with information and won the appeal. Obviously we didn't want him going back to the school that had failed him and he has been at his new school for over a year and is doing brilliantly.
You have to fight for what you want. If you stand up to the authorities you can make progress. I wish you and your son best wishes for the future. Don't give up, if you don't help your son, nobody else will.