It depends how the teacher handles writing numbers backwards and has him rewrite them. It is still really developmentally normal in first grade to write things backwards. I saw still quite a few kids do it up through second grade, and not so many by third grade.
Practicing writing the numbers correctly can help. If it's done in a positive way, it doesn't have to be punishment. My son has a documented processing disorder (in addition to being hearing impaired)- he has extra time for tests on his IEP, but we have never used it. Lots and lots of extra time at home on math facts, writing, etc. have gotten him "fast enough" so that he can take tests without the accomodation, which is better in the long run for him.
