Strictly speaking, developmental delay is not mental retardation. Clinically, developmental delay mainly refers to delayed growth in height and weight, and has no obvious relationship with intelligence. However, mental retardation cannot be directly considered as mental retardation, but should be evaluated to determine whether the speech and cognition are at the same level as they should be when compared to children of the same age. Detailed comparisons to peers will be made in the assessment scales, including the three major areas of motor, intellectual and social adjustment, as well as the developmental quotient. A percentile curve is used to determine whether the child is developmentally delayed and, if so, whether there is a combination of other disorders, such as autism. If the child is mentally and linguistically delayed, speech and language intervention is required, otherwise the child may become mentally retarded in the future. There are different levels of mental retardation in children, but early rehabilitation and language training is the only and essential way. There are two types of early speech and language rehabilitation, one is institutional rehabilitation and the other is home rehabilitation. The earliest period of home rehabilitation at 11 months of age can determine whether a child is mentally retarded by whether he or she can pronounce mommy and daddy, complete simple commands, and understand others and respond with facial expressions. At one and a half years of age, the child will show an increase in vocabulary of approximately 4 to 50 words, and at this time it is possible to further determine if there is a delay in language development. If there is not an explosive increase in vocabulary between the ages of one and a half and two years, there is usually a tenfold increase, meaning that a child who was saying 10 words should now be saying 100 or 20. This is the time to be alert for developmental delays. Without good instructional training, vocabulary imitation training, and social cognitive training at this time, the consequences of mental retardation can be severe if it does occur in the future. Therefore, mental retardation is not the only way for a child to end up with mental retardation, and early intervention can be used to prevent developmental delays from becoming mental retardation.