I am sorry you are going through this and I understand your frustration. What has the first grade teacher said to you? It must be clear to her that your son belongs at least in the 2nd grade. Can you ask her directly to recommend it?
We were lucky that our school skipped our kiddo after only the first two weeks of school (it was a private school), but it only took about 4 more months to realize that this would not be adequate.After one year of school I pulled him out and now homeschool. The school told me that he would plateau out- has not happened yet. Best wishes!