Intellectual disability involves a greater than average difficulty in learning.

A person is considered to have an intellectual disability when the following factors are present: general intellectual functioning is significantly below average; significant deficits exist in adaptive skills and the condition is present from childhood (eighteen years or less.
The signs of intellectual disability are often evident by a child’s first or second year. However, for some children diagnosed later as having a mild intellectual disability, the signs may not come to light until their school years when they have been formally tested.

Children with intellectual disability lag behind their peers in developmental milestones such as sitting up, smiling, walking and talking. They demonstrate lower than normal levels of interest in the environment and in responsiveness to others.

They are slower than other children in reacting to visual or auditory stimulation. By the time a child reaches the age of two or three, intellectual disability can often be determined using physical and psychological tests. Testing is important at this stage if a child shows signs of developmental delay.

Alternative causes such as impaired hearing may be found and treated. Diagnosis is highly dependent on a comprehensive personal and family medical history, a complete physical examination and a careful developmental assessment of the child
Children with intellectual disabilities (sometimes called cognitive disabilities or, previously,  mental retardation) may take longer to learn to speak, walk, and take care of their personal needs such as dressing or eating.

They are likely to have trouble learning in school. They will learn, but it will take them longer. There may be some things they cannot learn.
A woman who drinks alcohol or gets an infection like rubella during pregnancy may also have a baby with an intellectual disability.
intellectual disability is caused by abnormal genes inherited from parents.
They can also be caused by extreme malnutrition (not eating right), not getting enough medical care, or by being exposed to poisons like lead or mercury.
Intellectual disability can be caused by any condition that impairs the development of the brain before birth, during birth or in the childhood years. Many causes have been discovered, but in about one third of the people affected, the cause remains unknown.
An intellectual disability is not a disease. You can’t catch an intellectual disability from anyone. It’s also not a type of mental illness, like depression. There is no cure for intellectual disabilities.
However, most children with an intellectual disability can learn to do many things. It just takes them more time and effort than other children.
If the cause of a child’s intellectual disability is established, a prognosis can be made for the future of the child. Social and educational interventions can be planned that will make the best of the abilities of the child.
There is no cure for intellectual disability once it has occurred. Treatment and education programmes are geared toward helping children reach their full potential.

The sooner the diagnosis is made, the more the child can be helped. With infants, the treatment emphasis is on sensory-motor development, which can be stimulated by exercises and special type of play.