Intellectual disability usually manifests in the early stages of a child's development, and is characterized by a child being slow to master key processes such as talking, walking, potty training, dressing feeding; as well as with behavioral problems such as explosive tantrums or the inability to connect actions with consequences. Difficulties may occur in learning, communication, social, academic, vocational and independent living skills.

Intellectual disability affects a child's intellectual functioning and adaptive behavior. General intellectual functioning is typically measured by an intelligence test. 

Adaptive behavior refers to a person's adjustment to everyday life.

While children with intellectual disability may take more time to learn key processes, the degree of severity of the disability can vary considerably. This is why a comprehensive assessment including clinical and standardized testing should be used to determine the severity of impairment.