She also says that he doesn't approach the other kids to play with them, but sticks to himself a lot. It's seems that no matter what the situation is, it is my son who is at fault because he doesn't verbally express himself. I'm concerned that her obsession with this "communication problem" is going to negatively affect my son to the point that he doesn't want to go to school and his grades will suffer.
Talk with the school counselor. She may be able to give your son some individual time or include him in a small group on assertiveness. This will be important as your son moves to third grade, as both the curriculum and teacher expectations make a big jump from second to third.