Frustrated with son's school

My son is in 6th grade, and he is failing. He tries to do the best job he can. His biggest problem is his handwriting. The teachers wont accept his work when they cant read his handwriting. He tries and then he gets frustrated. He knows the work, or I think he does, can't really tell. I have asked for help with the teachers and the principal, they didn't really help much. He does go to after school tutoring when he isn't so upset. Usually he comes home and says he had a bad day because the teachers are mad at him. I don't want him to fail, he doesn't want to fail. I feel the teachers are failing him by not helping him. He can be very sensitive and takes this very hard. He goes to public school. All my boys have attended this school. He really wants to finish from this school as his brothers have. He does great in band, that is his favorite subject. He has a wonderful band teacher. Just cant get his other teachers to help. I don't think education has improved or changed for the better in the 20 years that I have had kids in school. It seems to be getting worse. Just not sure what to do.