My 6 Year Old Son Has A Lot Of Issues

My 6 year old son has a lot of issues controlling his anger and gets frustrated really easily. He also has issues focusing when there's other kids around. It's really noticeable in the classroom. This past school year he started saying he was going to stab his teacher, and he was going to slit his throat. He also talks about wanting to take his skin off. We carefully monitor what he's exposed to since he has these tendencies. He has seen a therapist about this, and we have worked closely with his teacher and guidance counselor to try and help him, but so far nothing has worked. Any ideas what might be going on and is there any medication that would help calm him down? I looked up symptoms of ADHD in 6 year old boys and it described him really well.