There are many forms of classification of children with mental retardation. In special education, two methods are widely used: grading according to intelligence level and educational possibility.

1. Graded according to intelligence level.

One classification method is to divide mental retardation into four grades according to IQ: mild, moderate, severe and extremely severe.

(1) first-degree mental disability (extremely severe): IQ below 25, poor adaptive behavior, and obvious facial dullness; All life needs the care of others; Motor sensory function is extremely poor, such as through training, only in the lower limbs, hands, jaw movement.

(2) Secondary mental disability (severe): the IQ value is between 25 and 39, and the adaptability is poor; Life ability is difficult to take care of itself even after training, and it still needs the care of others; Sports and language development are poor, and the ability to communicate with people is also poor.

(3) Third-degree mental disability (moderate): IQ is between 40 and 54. Incomplete adaptive behavior, incomplete performance of practical skills, such as self-care, simple housework, preliminary knowledge of health and safety, but poor reading and calculation skills; Poor ability to distinguish the surrounding environment, able to communicate with people simply.

(4) Level 4 mental disability (mild): IQ value is between 55 and 69. Adaptive behavior is lower than the average person's level; Have considerable practical skills, such as self-care, can undertake general housework and work, but lack skills and creativity; Generally, they can adapt to society under guidance. For example, with special education, they can acquire certain reading and computing skills. Have good ability to distinguish the surrounding environment; Can communicate with people more appropriately.

(Quoted from Handbook of Sampling Survey of Disabled Persons)