Hi Wipass
We went through the same problem many years ago with my eldest son - spent lots of time talking to 'specialists' and teachers, some of whom were effective, many of whom weren't. The biggest problem was the 'labelling' that came from people in authority who decided that he was clearly not capable of greater things.
Over a period of time, frustration and worry, we met an eye specialist who explained that many sufferers seem to have the same symptoms, where the eyes cannot focus on a specific point long enough for the word to be read in context. He went on to explain that for some of these sufferers, refresh rates on computer screens prompted the eyes to refocus on the word as a whole rather than just individual letters.
Seems crazy I know, but we went out and bought one of the first laptops and within weeks my son was reading as normal.
He is now 30 and has a company that writes 'coad' for many of the major mobile phone companies. Chances are, if you use a mobile the integration software was written by him.
We were lucky, but the same solution may work for your son. Whatever the situation, we quickly realised that as Lynx said, it should not be made a chore and we should remain positive and certainly not differentiate our son from his peers.
Regards