I think 16 to 84th percentiles are 'average' in that they are within one standard deviation of the mean. If you think of a bell curve, most of the population bunches up in the middle. That's why schools work in general.
You can try teaching him 'how to read' without reference to visual images. Just by talking about letters and what sounds they make and 'what word to you get when you put a 'c' with an 'a' with an 'r.' What if you put a 'b' in front of the 'ar?'
I guess you'd have to check that he knows the letters first, by asking 'how many letters can you name with no straight lines?' How many have no curves or circles?'
I would only try it if you can keep it 'fun' - perhaps while waiting in line at the grocery store, during car rides, as a way to pass the time.
Good luck!
Grinity
