[lepton]

RE kids not reading by the 2nd grade.. having some knowledge of this.. many times it's not the kid it's the curriculum..the method of teaching reading.. do a search on outcome based education.

In some cases it's neither...it's brain structure.

Through about age seven the brain is still undergoing major wiring changes (some of which begin again at onset of puberty). Seeing is not simply optics. There is an interpretaional level where the brain learns how to compute things like vertical and horizontal lines, depth, and patterns. Much of this basic learning is structural guided by environmental input.

It's like "late-talkers", sometimes there's a problem, sometimes the brain just isn't wired for it yet. Many loquatious and brilliant people have been "late-talkers".

[Zipporah]

..you are speaking of a very small minority.. the vast majority of kids who cannot read or are functionally illiterate is due to teaching methodology.