Mental retardation means substantial limitations in age-appropriate intellectual and adaptive behavior. It is seldom a time-limited condition. Although many individuals with mental retardation make tremendous advancements in adaptive skills (some to the point of functioning independently and no longer being considered under any disability category), most are affected throughout their life span (Hawkins, Eklund, James & Foose, 2003).

Many children with mild retardation are not identified until they enter school and sometimes not until the second or third grade, when more difficult academic work is required. Most students with mild mental retardation master academic skills up to about the sixth-grade level and are able to learn job skills well enough to support themselves independently or semi-independently. Some adults who have been identified with mild mental retardation develop excellent social and communication skills and once they leave school are no longer recognized as having a disability.

Children with moderate retardation show significant delays in development during their preschool years. As they grow older, discrepancies in overall intellectual development and adaptive functioning generally grow wider between these children and age mates without disabilities. People with moderate mental retardation are more likely to have health and behavior problems than are individuals with mild retardation.

Individuals with severe and profound mental retardation are almost always identified at birth or shortly afterward. Most of these infants have significant central nervous system damage, and many have additional disabilities and/or health conditions. Although IQ scores can serve as the basis for differentiating severe and profound retardation from one another, the difference is primarily one of functional impairment.

Cognitive Functioning

Deficits in cognitive functioning and learning styles characteristic of individuals with mental retardation include poor memory, slow learning rates, attention problems, difficulty generalizing what they have learned, and lack of motivation.

Memory.  Students with mental retardation have difficulty remembering information. As would be expected, the more severe the cognitive impairment, the greater the deficits in memory. In particular, research has found that students with mental retardation have trouble retaining information in short-term memory (Bray, Fletcher, & Turner, 1997). Short-term memory, or working memory, is the ability to recall and use information that was encountered just a few seconds to a couple of hours earlier—for example, remembering a specific sequence of job tasks an employer stated just a few minutes earlier. Merrill (1990) reports that students with mental retardation require more time than their nondisabled peers to automatically recall information and therefore have more difficulty handling larger amounts of cognitive information at one time. Early researchers suggested that once persons with mental retardation learned a specific item of information sufficiently to commit it to long-term memory—information recalled after a period of days or weeks—they retained that information about as well as persons without retardation (Belmont, 1966; Ellis, 1963).

More recent research on memory abilities of persons with mental retardation has focused on teaching metacognitive or executive control strategies, such as rehearsing and organizing information into related sets, which many children without disabilities learn to do naturally (Bebko & Luhaorg, 1998). Students with mental retardation do not tend to use such strategies spontaneously but can be taught to do so with improved performance on memory-related and problem-solving tasks as an outcome of such strategy instruction (Hughes & Rusch, 1989; Merrill, 1990).

Learning Rate.  The rate at which individuals with mental retardation acquire new knowledge and skills is well below that of typically developing children. A frequently used measure of learning rate is trials to criterion—the number of practice or instructional trials needed before a student can respond correctly without prompts or assistance. For example, while just 2 or 3 trials with feedback may be required for a typically developing child to learn to discriminate between two geometric forms, a child with mental retardation may need 20 to 30 or more trials to learn the same discrimination.

Because students with mental retardation learn more slowly, some educators have assumed that instruction should be slowed down to match their lower rate of learning. Research has shown, however, that students with mental retardation benefit from opportunities to learn to “go fast” (Miller, Hall, & Heward, 1995).

Attention.  The ability to attend to critical features of a task (e.g., to the outline of geometric shapes instead of dimensions such as their color or position on the page) is a characteristic of efficient learners. Students with mental retardation often have trouble attending to relevant features of a learning task and instead may focus on distracting irrelevant stimuli. In addition, individuals with mental retardation often have difficulty sustaining attention to learning tasks (Zeaman & House, 1979). These attention problems compound and contribute to a student’s difficulties in acquiring, remembering, and generalizing new knowledge and skills.

Effective instructional design for students with mental retardation must systematically control for the presence and saliency of critical stimulus dimensions as well as the presence and effects of distracting stimuli. After initially directing a student’s attention to the most relevant feature of a simplified task and reinforcing correct responses, the complexity and difficulty of the task can gradually be increased. A student’s selective and sustained attention to relevant stimuli will improve as he experiences success for doing so.

Generalization of Learning.  Students with disabilities, especially those with mental retardation, often have trouble using their new knowledge and skills in settings or situations that differ from the context in which they first learned those skills. Such transfer or generalization of learning occurs without explicit programming for many children without disabilities but may not be evident in students with mental retardation without specific programming to facilitate it. Researchers and educators are no longer satisfied by demonstrations that individuals with mental retardation can initially acquire new knowledge or skills. One of the most important and challenging areas of contemporary research in special education is the search for strategies and tactics for promoting the generalization and maintenance of learning by individuals with mental retardation. Some of the findings of that research are described later in this chapter and throughout this text.

Motivation.  Some students with mental retardation exhibit an apparent lack of interest in learning or problem-solving tasks (Switzky, 1997). Some individuals with mental retardation develop learned helplessness, a condition in which a person who has experienced repeated failure comes to expect failure regardless of his or her efforts. In an attempt to minimize or offset failure, the person may set extremely low expectations for himself and not appear to try very hard. When faced with a difficult task or problem, some individuals with mental retardation may quickly give up and turn to or wait for others to help them. Some acquire a problem-solving approach called outer-directedness, in which they seem to distrust their own responses to situations and rely on others for assistance and solutions.

Rather than an inherent characteristic of mental retardation, the apparent lack of motivation may be the product of frequent failure and prompt dependency acquired as the result of other people’s doing things for them. After successful experiences, individuals with mental retardation do not differ from persons without mental retardation on measures of outer-directedness (Bybee & Zigler, 1998). The current emphasis on teaching self-determination skills to students with mental retardation is critical in helping them to become self-reliant problem solvers who act upon their world rather than passively wait to be acted upon (Wehmeyer, Martin, & Sands, 1998).

Adaptive Behavior

By definition children with mental retardation have substantial deficits in adaptive behavior. These limitations can take many forms and tend to occur across domains of functioning. Limitations in self-care skills and social relationships as well as behavioral excesses are common characteristics of individuals with mental retardation.

Self-Care and Daily Living Skills.  Individuals with mental retardation who require extensive supports must often be taught basic self-care skills such as dressing, eating, and hygiene. Direct instruction and environmental supports such as added prompts and simplified routines are necessary to ensure that deficits in these adaptive areas do not come to seriously limit one’s quality of life. Most children with milder forms of mental retardation learn how to take care of their basic needs, but they often require training in self-management skills to achieve the levels of performance necessary for eventual independent living.

Social Development.  Making and sustaining friendships and personal relationships present significant challenges for many persons with mental retardation. Limited cognitive processing skills, poor language development, and unusual or inappropriate behaviors can seriously impede interacting with others. It is difficult at best for someone who is not a professional educator or staff person to want to spend the time necessary to get to know a person who stands too close, interrupts frequently, does not maintain eye contact, and strays from the conversational topic. Teaching students with mental retardation appropriate social and interpersonal skills is one of the most important functions of special education.

Behavioral Excesses and Challenging Behavior.  Students with mental retardation are more likely to exhibit behavior problems than are children without disabilities. Difficulties accepting criticism, limited self-control, and bizarre and inappropriate behaviors such as aggression or self-injury are often observed in children with mental retardation. Some of the genetic syndromes associated with mental retardation tend to include abnormal behavior (e.g., children with Prader-Willi syndrome often engage in self-injurious or obsessive-compulsive behavior). In general, the more severe the retardation, the higher the incidence of behavior problems. Individuals with mental retardation and psychiatric conditions requiring mental health supports are known as “dual diagnosis” cases. Data from one report showed that approximately 10% of all persons with mental retardation served by the state of California were dually diagnosed (Borthwick-Duffy & Eyman, 1990). Although there are comprehensive guidelines available for treating psychiatric and behavioral problems of persons with mental retardation (Rush & Francis, 2000), much more research is needed on how best to support this population.

Positive Attributes

Descriptions of the intellectual functioning and adaptive behavior of individuals with mental retardation focus on limitations and deficits and paint a picture of a monolithic group of people whose most important characteristics revolve around the absence of desirable traits. But individuals with mental retardation are a huge and disparate group composed of people with highly individual personalities (Smith & Mitchell, 2001b). Many children and adults with mental retardation display tenacity and curiosity in learning, get along well with others, and are positive influences on those around them (Reiss & Reiss, 2004; Smith, 2000).