I hope these ideas don't sound terrible when they're out there in cyber space but...I want to try to help because I understand how that knot in your stomach feels. Last year my colleague (we teach first grade) got a very oppositional and defiant child...rolling around on the carpet, screaming and shouting out, refusing to sit down, hitting others, you name it!! The first two weeks were BRUTAL but then she just totally started ignoring him ... it sounds easier than it was. She didn't make eye contact with him, talk to him or include him in anything at all. The class went on it's merry way (and I think some of the little ones were grateful for the break from redirecting this kid). She stopped ignoring him when he joined the group and was productive, you know, positive reinforcement in the form of attention and inclusion. He was starving for that type of attention but only knew how to get the negative type. It took awhile and a lot of patience, but he was so lovely at the end of the year. He really started to care about being a productive member of the class.
Oh...and when he got WAY TOO out of control to ignore, she would silently and quickly write a note to me (across the hall) and send it over with another student. She never said a word to the student in question. Then when I had a second, I would walk calmly across the hall, take the child by the hand and lead him to my classroom. Thank goodness that the element of surprise caught him off guard and he never refused to come with me. Maybe that part was just luck!!
GOOD LUCK TO YOU!!! Just know that this little one ended up being one of my friend's favorites (even though we're not supposed to have any).