My son is having a hard time at school with his writing?

Okay my child is 6 years old. His writing is just terrible. He is is going to occupational therapy for it as well. He is very smart but,when he writes it just comes out really bad. Well his teacher is kind of getting mad with him even made him put his head down on the desk so he can calm down and try again neatly when he was writing something. She is keeping reminding me how poor his writing is. we are all trying hard to correct him he's also getting the help he needs. Well my fear is she's going to try to use that to keep him back a year when i know he's smart. Again it's just his writing. In a way I can see her fustration but, I also don't want her getting mad at him because that's what he's is getting help for. Any advice?