Thanks, that helps. I guess I wouldn't think of being one standard deviation below the mean as "average" but I suppose that is what they meant. 16th percentile seems problematic to me, especially when I am pretty sure his understanding and reasoning are above the mean.

He does know pretty much all his letters, and quite a few phonems (he is learning to read in French, so there are a lot of these), but seems to panic when they are all in a row in a long word.