Intelligence testing is an effective tool for assessing a child’s cognitive development and social adjustment, providing an understanding of the child’s current level of development and a general prediction of the child’s future, and is essential in the evaluation of children with intellectual disabilities. Mental retardation or mental retardation is a common sequela of children with brain injury. The medical term “mental retardation” refers to a disability that begins before the age of 18 and is characterized by significant limitations in intellectual and adaptive behavior, with adaptive behavior manifested by a lack of conceptual, social, and practical adaptive skills. A well-developed child has an average IQ between approximately 80-120 and a total score of 150. If the measured IQ is between 70 and 80, it is referred to as a critical state and requires further testing to clarify the presence of mental retardation to determine whether dynamic observation or early intervention is indicated. The severity of children with intellectual disability is divided into four levels based on the measured IQ level: mild: 70-50 IQ, moderate 50-35 IQ, severe 35-20 IQ, and very severe less than 20 IQ. There is a little variation from scale to scale. Children with mental retardation are usually accompanied by deficits in adaptive behavior, which is the function of functioning effectively in daily life and is related to life skills. Children with mild mental retardation show some mild developmental delays before school age, most of which are not detected until they enter school or develop some behavioral problems, acquire good language skills, are fluent, lack advanced thinking skills, acquire some vocational skills, and have a developmental potential roughly equivalent to a normal child between the ages of 6 and 12. Children with moderate mental retardation can often be identified in preschool, before the age of 6. They are consistently behind in language and social skills, have poor social awareness, tend to have average motor development, and can have some simple self-care skills. They can initially communicate only with single words or gestures and eventually can communicate using simple sentences and can develop the most basic self-care skills as well as reading and writing. The developmental potential is roughly equivalent to that of a normal child between the ages of 3 and 6. Children with severe mental retardation can be identified in infancy and up to 1 year of age. They are severely underdeveloped, have poor motor function development, and have only minimal language skills. Self-care skills are severely deficient and are likely to be undeveloped by 4-5 years of age. They will be able to speak 1-3 word sentences in the future and can eventually acquire the ability to care for themselves under full supervision. The developmental potential is roughly equivalent to that of a normal child under 3 years of age. Children with very severe mental retardation, also identified within 1 year of age, have only minimal sensorimotor skills and require full supervision and care. These children may be able to sit, make some sounds, understand single words and recognize familiar people. They may develop some motor skills such as standing or walking as they get older, but they require complete care and supervision in their daily lives. The above prognosis for children with mental retardation refers only to children with simple mental retardation, not to children with other conditions such as cerebral palsy. Since early intervention for children with brain injury can significantly improve the prognosis, early IQ test results only indicate the current status of the child, not the final prognosis of the child. As the old saying goes, the child’s intelligence test results are relatively stable after the age of 3 and can be used as a basis for assessing the child’s future. Therefore, it is important for a child with mental retardation to have an IQ test to understand the child’s status and to seize the golden treatment period before the age of 3, especially before the age of 1, to improve the child’s prognosis and give the child a better future.