Estimated prevalances of five specific learning difficulties (data from Science, April 19, 2013)

NIH research funding for these SLDs in 2000-2009 varied widely


SLD                           Estimated prevalence (%)   NIH research funding in US $1000s
Dyslexia                                           4-8                                              27,283
Dyscalculia                                       3.5-6.5                                          1,574
ADD/ADHD                                    3-6                                            532,800
Autism spectrum disorder                  1                                               851,270
Specific language impairment            7                                                28,611



Of course co-occurence of these learning disabilities occurs more often than not, however the funding for research does seem somewhat one-sided for a very small population of children.