The problem may not be with your son but with the school system. He simply may not be ready. The fault likely isn't with you or your child but with the expectations of the education system these days. Not only weren't children expected to know numbers, letters or how to spell their names back in the old days when I was a kid, the education system actively discouraged parents from teaching it. Virtually all kids learned to read in first grade, the exception being those with what we now know of as learning disorders.
If you do any search for statistics you will find that there is no positive correlation between literacy and age at which reading is taught.
