My DD did this for a little while this past year. I found it odd since she has been able to write with no problems. It wasn't until I talked to another mom that I found out her DD does it but she doesn't seem to be doing it for fun. DD sat across from her so I guess she was mocking her. I did talk to her and explained how her friend is trying to learn how to write and she needed to help her writing the correct way. Since then we haven't had any mirror image writing at school but on occasion she will do it at home ... just for fun.