I used to organize the major annual training institute for the Montana Association of School Psychologists. Our institutes last for two-and-a-half days, all on a single topic, and all presented by just one speaker. I tried to get David Geary to come to present to us, having had a chance to visit with him at a major conference in Chicago in the late 1990s, but he declined, on the grounds that no one in the entire world knew enough about math disabilities to present for that much time. Finally, in 2011, after calling a bunch of top researchers, I was able to bring Michele Mazzocco from Johns Hopkins to talk to us. We still do not know much, but we are finally getting some good research.
David Geary was lead author on the National Panel report on math learning processes in - I think - 2009, and that is available for free on line. A book that I like a lot is Dehaene, S. The Number Sense: How the Mind Creates Mathematics. (OUP - not sure what the current edition is). He is working in France but writes brilliantly in English and for a geek like me the book is laugh-out-loud funny in parts. He also had a terrific article in Science on sources of mathematical thinking. It is a little bit older information but it is solid. If you are a member of AAAS you can find it on line.
http://www.newyorker.com/magazine/2008/03/03/numbers-guy
