Adaptive behavior is developed over a period of time and is a function of both mental/intellectual and social/emotional skills and abilities. By definition, mentally retarded people are significantly limited in terms of their adaptive functioning in at least two of the following areas: communication, self-care, home living, social/interpersonal skills, community resource use, self-direction, academic skills, work, leisure activities, health, and safety. These limitations significantly interfere with an individual's ability to navigate through many everyday situations.

Deficits in adaptive functioning are identified with standardized testing and comparison against general population norms. Scores falling two standard deviations below average (representing about 2.5 percent of the population) suggest that significant adaptive limitations are present. There are three types of adaptive behavior: social, conceptual, and practical. Scores that fall at least two standard deviations below the mean (average) in any one of the three areas suggest a deficiency. In addition, an individual is demonstrating deficiency in adaptive functioning if his score falls at least two standard deviations below the mean in his overall score on a standardized measure of social, conceptual, and practical skills.

Borderline Intellectual Functioning

The intellectual deficits characteristic of the mentally retarded population vary widely. Some very mild cases of intellectual deficit are not appropriately classified as instances of mental retardation, but instead are better described by the diagnosis of Borderline Intellectual Functioning diagnosis, which can be made when IQ scores fall between 70 and 84. Such IQ scores describe uncommonly low intellectual ability, which is nevertheless not low enough to qualify for a diagnosis of mental retardation. This classification describes a group comprising about 7 percent of the general population that falls into an area of delayed intellectual, emotional, and/or adaptive functioning that teeters on the edge of mental retardation but does not actually qualify for that specific diagnosis. Like mental retardation, borderline intellectual functioning is a classification, not a specific disease.

Borderline intellectual functioning is not well known; its obscurity lies in its 'neither here nor there' nature. While such individuals function at a higher level than those classified as mentally retarded, their cognitive functioning is nevertheless limited, creating problems for everyday functioning, judgment, and academic or occupational achievement. People qualifying for a borderline intellectual functioning diagnosis are at a disadvantage when entering unfamiliar and stressful situations, but at the same time function well enough to make it difficult to determine definitively that there is a deficit present requiring assistance.

The subtle nature of borderline intellectual functioning is further complicated by terminology. Formerly known as borderline mental retardation, the condition's new title may prevent affected individuals from being recognized as having deficits that require services from mental health or mental retardation organizations. Deficits often go unnoticed until affected individuals reach school settings or other demanding and unfamiliar environments. There, the condition manifests itself in poor academic performance, lack of attention to tasks, and behavioral problems, which may stem from frustration and emotional immaturity.