Mathematics is a difficult subject for a lot of children to grasp. Not concentrating in class maybe due to many different variables. Autism has other significant indicators which I would also be looking for...how does he relate to others in his school, and school playground, and other social settings... I am also querying why his teacher has selected Autism Spectrum as the cusp of the behavior. If he is reading well and able to concentrate on reading chapters of a book, concentration doesn't seem to predominate the child's behavior. Literacy skills are at an all time low in schools, with many students in later school years leaving with poor levels of reading skills and comprehension and writing skills which are also very poor. Some children with Autism can have areas where they can excel, and can become obsessive, however I am thinking have your young fellow checked for all Spectrum disorders, just to be sure, then get his eyes tested. Its easier to see what is in front of you.