34 Neurodevelopmental DisordersTABLE 1 Severity levels for intellectual disability (intellectual developmental disorder)
Severity 
level Conceptual domain Social domain Practical domain
Mild For preschool children, there 
may be no obvious conceptual 
differences. Fo r school-age 
children and adults, there are 
difficulties in learning aca-
demic skills involving reading, 
writing, arithmetic, time, or 
money, with support needed 
in one or more areas to meet 
age-related expectations. In 
adults, abstract thinking, exec-
utive function (i.e., planning, 
strategizing, priority setting, 
and cognitive flexibility), and 
short-term memory, as well as 
functional use of academic 
skills (e.g., reading, money 
management), are impaired. 
There is a somewhat concrete 
approach to problems and 
solutions compared with 
age-mates. Compared with typically developing age-
mates, the individual is immature in social 
interactions. For example, there may be diffi-
culty in accurately perceiving peers’ social 
cues. Communication, conversation, and lan-
guage are more concrete or immature than 
expected for age. There may be difficulties reg-
ulating emotion and behavior in age-appropri-
ate fashion; these difficulties are noticed by 
peers in social situations. There is limited 
understanding of risk in social situations; 
social judgment is immature for age, and 
the person is at risk of being manipulated 
by others (gullibility).The individual may functi on age-appropriately in 
personal care. Individuals need some support with 
complex daily living tasks in comparison to peers. In 
adulthood, supports typicall y involve grocery shop-