Meet with the principal, tell them he's distressed (and describe incidents specifically), and ask for their help. Also give them this information in writing. They may want to do an evaluation, which will take time, but there may be short-term strategies they can use immediately (give him "break tickets" so he can escape for a few minutes before he gets to crisis mode?).
Don't reward/punish at home what happens at school. You can talk about it or debrief but let school reward/punish. You have enough to do at home, and he should see you as a supporter, not as an extension of the teachers.
At this age, don't tie huge rewards to large sudden improvements in behavior: the huge reward increases the anxiety and diminishes the chance of success. We did this for a while and it made everything worse for us.
But do follow through on the Wii this time; it's important that you be consistent and keep your word.
HTH,
DeeDee
