the more i think about and read this thread the more it convinces me that your DS should not have been excluded.
if this had been my DS in mainstream he would have
a, been delighted at a day off and possibly want to do it again to get another day off
b, extremely angry at the injustice of the punishment and focus his emotions and anger towards the other person who had tried to rip up his work
c, his confidence and self esteem would have hit the floor and he would probably have become depressed after the anger would have subsided.
agree with amber there should be a plan in place and this should be in his statement,something along the lines of a quiet place to go to when DS is becoming stressed etc.
at DS school when they spot a child becoming distressed they remove the child from the situation straightaway,a lot of the time they take them for a walk,to burn off the energy, and to calm them down,something so simple like that would be beneficial.