My heart really goes out to you!  We were in that position last year in Kindergarten with my DSthen6.  He was just *angry* at home, at school he was fine.  It was very confusing and frustrating because we felt so stuck and the school refused any changes for a K'er.  
I think I understood more what a caged animal felt like in that 3 months when we were fighting with the school than I ever have before.  Because DS *was* a caged animal, he paced at school, biding his time, and then he lashed out at us for putting him back in the cage over and over.
I also seriously considered professional help, but once we pulled DS from school the behaviors disappeared.  If moving him immediately hadn't been an option, I wouldn't have hesitated to find a psychologist who is understanding of GT kids.
((HUGS)), it's such a horrible situation to be in.  I still have quite a bit of anger towards the school and we've been gone a year.