An intellectual disability refers to people with an IQ below 55. A mild intellectual disability refers to a people with an IQ between 55 and 70. A mild to borderline intellectual disability refers to people with an IQ between 70 and 85. However, they only qualify as borderline intellectual disability if they also show limited adaptive functioning.

Limited adaptive functioning refers to deficits in adaptive functioning that result in failure to meet developmental and sociocultural standards for personal independence and social responsibility. Without ongoing support, it limits functioning in one or more activities of daily life (e.g. independent living).

Borderline intellectual functioning refers to slightly above the 70-75 IQ level with low normal functioning. There is, thus, a low level of adaptive functioning. With regard to adaptive functioning, there is a distinction between the conceptual domain (e.g. working memory), social domain (e.g. perspective taking) and practical domain (e.g. cooking). However, there is no clear consensus regarding the definition of adaptive functioning.

There are several characteristics of mild- to borderline intellectual disability:

1. Academic and cognitive skills
   1. Memory
      They have poorer memory skills (1), structural abnormalities in the phonological store (2), developmental lags in visuospatial and central executive subsystems (3). This is indicative of a working memory developing in line with their general intellectual abilities and not a qualitative deviation from development.
   2. Attention
      They have poorer attention shifting (1), cognitive inhibition (2), problem-solving (3), planning (4), response inhibition (5) and slower processing speed (6). Students with BIF tend to use more immature theories.
2. Motor skills
   Mild- to borderline intellectual disability is associated with motor problems although not everyone has this.
3. Social behaviour
   
   1. Social interaction
      There is more solitary play (1), less group-play behaviour (2) and peers have a greater impact on behaviour (e.g. more positive interaction when coupled with an average IQ peer) (3).
   2. Parenting
      There is less positive and less sensitive parenting. Parental understanding of problems of children with BIF may be inadequate.
   3. Antisocial behaviour
      There is more antisocial behaviour among boys but not among girls.
4. Mental health
   Mental health problems are more common and they are less likely to receive treatment. When they do, they are more likely to receive medication.
5. Employment and marriage
   Occupational prestige and income are lower (1), there is more unemployment among women compared to the general population (2) and adolescents have difficulty maintaining a job (3). The rate of marriage is lower at age 35 but not at age 50.

There is overrepresentation of limited adaptive functioning in forensic settings. Recidivism and multiple conducts occur more often among individuals with MBID.

Children with borderline intelligence are at risk for chronic educational failure (1), absence from school (2), repetition of grades (3) and dropout or expulsion from school (4). Suspension from school is one of the best predictors of delinquency. Individuals with MBID are not necessarily unmotivated.

Education is correlated with income, occupation and health. MBID have increased risks for educational, mental health and societal problems. There is increased risk for the development of mental disorders with MBID. A lot of people with MBID have problematic attachment. This is associated with adverse childhood experiences. This, in turn, increases the risk of neurological problems and risky behaviour. In short, individuals with MBID show more risk-taking in the presence of peers.

MBID is associated with cognitive control deficits. They struggle to make safe decisions under negative peer pressure.      There are also social-cognitive deficits in MBID and this could make individuals with MBID more vulnerable to peer pressure because they are less able to read their peers’ intentions.

In the presence of peers, MBID is associated with increased risk-taking and increased risk-taking propensity. It is also associated with lower behavioural consistency in the presence of peers. This indicates that MBID and peer influence result in lower behavioural consistency. MBID enhances safety estimates under peer pressure. Risk-taking may be more of a product of low intellectual functioning rather than behavioural problems, as people with behavioural disorders do not necessarily show increased risk-taking.

It is difficult to determine that someone has MBID as it is not directly visible and other symptoms (e.g. conduct problems) are often more prominent.

People with MBID appear to have impaired executive functioning. Besides that, they also show impairments in attention (e.g. divided attention; sustained attention), especially when the complexity of the task increases. There is a differential effect of time on individuals with MBID with regard to attention. Inhibition becomes more difficult when the task becomes more difficult. Everyone has poorer inhibition skills with a distractor but the individuals with MBID have more difficulties than controls. Individuals with MBID appear to have a ‘smaller’ working memory meaning that they will lose information from the working memory faster.

In short, individuals with MBID appear to have deficits on attention (1), executive functioning (2), processing speed (3), inhibition (4) and working memory (5). These deficits increase when the task becomes more complex.

Sexual delinquency and recidivism are more common in MBID. Stress influences either working memory or inhibition strongly in individuals with MBID. Peer pressure is a huge stressor for adolescents but it appears to be a stronger influence for individuals with MBID. It is believed that peer pressure is a stronger influence during adolescence due to the developmental lag of the prefrontal cortex compared to the limbic system. In individuals with MBID, the prefrontal cortex is less developed, meaning that peer pressure has a larger influence on individuals with MBID. The poorer development of the prefrontal cortex leads to fewer opportunities to regulate emotions.

Social adaptive functioning requires emotion recognition (1), understanding of emotions (2), perspective-taking and theory of mind (3), social skills (4) and problem-solving skills (5). This, thus, requires executive functioning. However, this is often impaired in adolescents with BIF, leading to impaired social adaptive functioning.

Individuals with MBID often have poorer social adaptive functioning. They also more often have social anxiety disorder. People with MBID have poorer emotion recognition. People with MBID appear to have proper basic perspective-taking. They lag behind in the development of perspective-taking but they seem to catch up. However, with more complex perspective-taking (i.e. needed for social adaptive functioning), people with MBID perform worse.
Perspective-taking worsens with stress in individuals with MBID. Children with deviant behaviour (e.g. aggression) are often rejected by peers. This increases stress levels, which adds to the vicious cycle as this decreases perspective-taking. In short, adolescents with MBID more often experience stress.

People with MBID have more failures (1), are less able to read the others’ intentions (2) and are less able to anticipate (3). Executive functioning and social adaptive functioning are related because they partially draw on the same mechanisms (e.g. perspective-taking). The transition from adolescence to adulthood may be problematic for people with MBID.

The risk of MBID increased with low birthweight (1), poor family environment (2), low level of education of the mother (3), exposure to toxic metals (4), maternal drug use during pregnancy (5), familial history of intellectual disability (6) and mother’s illiteracy (7). Education (1), social contacts (2) and personal qualities (3) are protective factors for MBID. The social contacts include supportive parenting (1), role models for achievement (2) and warm relationships (3).

MBID might not lead to a noticeable difference but it will lead to noticeable damage to the individual. However, early training and training with adolescents’ communication skills appear to be effective.