There are a number of areas in which a person can have problems: reading, math, writing, spelling, handwriting, etc. Most people are familiar with the term dyslexia, but this is simply another name for a Specific Learning Disability in the area of Reading.
It is thought that dyslexia affects 1 in 5 children, which in America means 10 million people, at least.
There is lots of information and misinformation out there about learning disabilities. To be sure that you get the correct information, be sure to go to accurate, research-based sources.
Here is a search list on learning disabilities. some information may be of help to you
Information on the assessment of learning disabilities can be found here.