Wii man, I'm sorry the staff at your school are so bad at their jobs. I know yours isn't the only school in that situation, but sometimes there are staff out there who do actually care. I remember many of the kids at my sons' primary school used to go and talk to the crossing warden if they had a problem. Not that she could do very much, but it was often enough that she had the time to listen and care. I was bullied too, and my teachers were the same as yours - all they were worried about was what grades I got. When
I worked as teaching assistant/youth worker, I always made a point of listening to the kids in my charge and watching out for anyone being bullied. I think it's something you're more attuned to if you've been bullied yourself. I wouldn't want anyone to go through what I had to.
Viva, if you can afford it, riding is a great confidence booster, and a good socialiser too. Then there's swimming, which is a lot cheaper, and again, if your son joins a swimming club, he'll like as not make few like-minded friends and have a bloomin' good time (we used to tell the junior team that their coach was going to buy fish & chips all round if they won their galas).
Can I also cite music here? This is mainly because banding is my hobby and I've seen it make great changes in kids. Having done it for some years I've had the advantage of seeing timourous little beginners grow into confident, skilled young adults who are respected by everyone. There's a wide range of music, instruments and bands/orchestras out there - he's bound to find something to suit.