You need to talk with the teacher and find out more about the situation. Ask for a parent/teacher conference. If she refuses or says she doesn't have time, talk to the principal and insist on one. Indicate your willingness to come at any time that is convenient for the teacher. Try to go to the conference without being unduly defensive or accusatory. Express the attitude that you know she wants to help your son and you want to help in the process.
You say that your teacher is ignoring your son. Sometimes a teacher makes a point of ignoring unacceptable behavior while trying very hard to give children recognition and approval when they are doing well. Try to find out whether she praises him if he does pay attention.
And do your part at home. Make certain he gets enough sleep so that he isn't tired the next day in class. Often that means restricting TV in the evenings. Read to him—he is definitely not too old—and stop every page or two and ask him to tell you about the story. If he can't, urge him to listen more carefully.
If, after you try these things and other ideas of your own, he seems unhappy in school, says he doesn't want to go, claims to be sick, etc., you might talk to the principal about trying him in another classroom with a different teacher.
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.