We ended up calling the State Dept. of Ed on the phone, on the instruction of our advocate, and had them intervene in a situation that could not be turned around by our advocate or us despite a year of efforts. Once we found the right person to talk to, it was fairly straightforward and extremely helpful.
I wouldn't hesitate at the stage where you are to take this step; you have done all you can, and the teacher is mistreating your child, and the principal appears not to be stopping it. If your advocate recommends this course, you may want to write a letter to the principal first detailing the latest abuses when the para was out, so that that principal has every chance to fix it before you file the complaint. You want to be able to show that you did every possible step and the issue was not resolved.
DeeDee
