It wouldn't hurt to get it evaluated by a professional. Like one of the ladies, I, too, am dyslexic and it does take different forms in different people.
The sooner you as a parent know where his weaknesses are, you can help him develop methods to work around his problem and just be supportive and understanding.
If he is dyslexic, the sooner he knows, the sooner he can realize that he isn't the only person who flips numbers around or turns his "b" into a "p"and didn't see it until he goes back to proofread it.
There is power in knowing that you aren't the only one who struggles with these issues. I have issues with it, but not as severe as my dad. That makes coping with it easier and I know that he understands when I talk about how I told someone (for instance) that the address was 650 when the address was really 560 ABC street.
There are a lot of resources out there, so take advantage of them.