My son is in the 5th Grade and he started off the year doing the same thing. He would do his homework in the afterschool program but I was later told by his ELA teacher that he refused to read in class. I was so sad and frustrated. I asked him why he refused to read in class and he said it is hard for him to keep up with the class while reading the book. He has an IEP but it still feels like some of the teachers have little knowledge of ADHD and the classic symptoms. I signed him up for extra help for the subjects he finds most difficult. The teachers said that he is improving. I told him that if he refuses to read then he cannot play video games at home. I told him that trying is the most important thing he can do and that asking for help is more than ok.
I also have ADHD so it is really hard for me to keep the pace going but I do my best. Maybe your son can read the audio books? That was an alternative for my son and it helped him follow along with the story.
Keep the line of communication open with all of his teachers and give yourself a pat on the back. It is not easy so remember to be kind to yourself when it gets rough.