People differ in how clever they are. Some people can learn a wide range of complex skills with ease, while others find learning even comparatively simple skills very difficult. When someone has learning difficulties of a general nature they may be described as mentally handicapped. In the past, a variety of terms that we would now consider offensive have been used to describe individuals with learning difficulties, such as natural fools, idiots, morons, slow-witted or feeble-minded. Whatever term is used it is generally agreed that mental handicap affects the individual’s capacity to learn. Mental handicap results in people having incomplete, or arrested development of intellectual capacities. People with severe learning difficulties are most commonly described in terms of a lack of general intelligence or mental capacity, and a resulting impairment of mental development and learning. IQ tests are central to our current definitions of learning difficulties.