Mental retardation refers to below-average intelligence. The diagnosis of mental retardation is based on intelligence quotient (IQ) tests and a child's learning problems.

Mental retardation is categorized according to IQ scores:

• In mild retardation, IQs range from 50 or 55 to 70.
• In moderate retardation, IQs range from 35 or 40 to 50 or 55.
• In severe retardation, IQs range from 20 or 25 to 35 or 40.
• In profound retardation, IQs are below 20 or 25.

Children with mental retardation may have difficulty with:

• Learning, especially complex tasks.
• Language. Children with severe mental retardation have more difficulty learning language than children with mild to moderate mental retardation.
• Self-care (in cases of severe mental retardation).