Learning disabilities are disorders that affect one's ability to understand or use spoken or written language, do mathematical calculations, coordinate movements, or direct attention. Although learning disabilities occur in very young children, disorders are usually not recognized until a child reaches school age. Research shows that 8 to 10 percent of American children under the age of 18 have some type of learning disability. Learning disabilities affect one's ability to interpret what one sees and hears or to link information from different parts of the brain. These limitations can show up as specific difficulties with spoken and written language, coordination, self-control, or attention. Such difficulties extend to schoolwork and can impede learning to read or write or to do math. Learning disabilities do not reflect IQ (intelligence quotient), or how smart a person is.