The present classification divides retardation into mild, moderate, severe, and profound. These categories, along with specific characteristics for each category, are shown below.
MILD RETARDATION (IQ 50-70): People are not noticed as retarded by the casual observer. They can acquire practical skills and useful reading and arithmetic to sixth-grade level. They can usually achieve social and vocational skills necessary for self-maintenance but is slower to walk, feed themselves, and talk than most children. They can be guided toward social adjustment. They may need occasional guidance and support when under unusual social or economic stress.
MODERATE (IQ 36-50): People under this category show more delay in motor especially in speech. They respond to training in various self-help activities. They can learn simple communication, can perform simple tasks under elementary health and safety habits, and sheltered conditions; participates in simple manual skills; does not progress simple recreation; travels alone in familiar places; usually incapable of self-maintenance.
SEVERE RETARDATION (IQ 20-35): These people exhibit marked delays in motor development; little or no communication skill; may respond to training in the elementary self-help, for example, self-feeding. Usually walks, barring specific disability, has some understanding of speech and some response; can profit from systematic habit training, can conform to daily routines and repetitive activities; needs continuing direction and supervision in a protective environment.
PROFOUND RETARDATION (IQ below 20): Under this category, there is gross retardation; minimal capacity for functioning in sensorimotor areas; obvious delays in all areas of development; shows basic emotional responses; may respond to skillful training in the use of legs, hands, and jaws; needs close supervision, may walk, need nursing care, have primitive speech, usually benefits from regular physical activity; incapable of self-maintenance.
Mental retardation has many causes. Some are genetic accidents, such as Mongolism or Down’s syndrome, which are caused by an extra chromosome. Some are caused by physiological problems, such as cretinism, which results from thyroid deficiency. Some are due to physical factors such as not receiving enough oxygen before birth. And many are simply a combination of hereditary and environmental factors – the parents were retarded and did not provide a stimulating home environment for the children.