How do you know if you have a learning disability?

School . Most people with a learning disability present in school with grades or achievement less than expected for their intellect. A learning disability is a neurological condition that interferes with a person’s ability to store, process, or produce information. From http://www.Ldanatl.Org/new_to_ld/defining.Asp.
Problem/testing. First, do you have an area of academic functioning which is much harder for you than for other people your age and general level of intelligence? If so, then testing can determine how great the gap is between your overall IQ and your abilities in that particular area--reading, math, writing, e.g. Ld requires a large gap between those two numbers. Finding calculus hard, e.g., would not count.