Terms such as learning disorder and learning disability often are used interchangeably, although the latter term is used more commonly. A major stride in the definition of learning disabilities came from the National Joint Committee for Learning Disabilities. The National Joint Committee for Learning Disabilities defined a learning disability as a generic term that refers to a heterogeneous group of disorders manifested by significant difficulties in the acquisition and use of listening, speaking, reading, writing, reasoning, or mathematical abilities. These disorders are intrinsic to the individual and presumed to be due to central nervous system dysfunction. Even though a learning disability may occur concomitantly with other handicapping conditions (e.g., sensory impairment, mental retardation, social and emotional disturbance) or environmental influences (e.g., cultural differences, insufficient/inappropriate instruction, psychogenic factors), it is not the direct result of those conditions or influences (Hammill et al. 1981, p. 336).