What are the causes of intellectual disabilities in children, and how are they assessed?
Diagnostic assessment is usually going to focus on two major areas: intellectual functioning and adaptive functioning. There will also be a focus on whether these two major areas had deficits or impairments during the developmental period. This can be done with a record review, interviews, and psychological testing (such as intelligence testing).
I think some of the causes are genetic/chromosomal and others often relate to prenatal factors. Disease, toxic exposure, infection, and malnutrition have all been shown to be causative for intellectual disability.