The critical period hypothesis is the hypothesis that there is a specific period of time during which language can be acquired most easily. This period is typically thought to begin around birth and end around puberty.

There is a variety of evidence that supports the critical period hypothesis. This evidence includes studies showing that children who are exposed to two languages from birth are more likely to become bilingual than children who are exposed to two languages later in life, studies showing that children who are raised in multilingual environments are more likely to have difficulty learning a new language than children who are raised in monolingual environments, and studies showing that children who are deaf from birth are more likely to have difficulty learning a spoken language than children who are deaf later in life.

The implications of the critical period hypothesis for language education are that children should be exposed to a variety of languages as early as possible, children should be taught a foreign language as early as possible, and children who are deaf should be taught a sign language as early as possible.

There are a number of criticisms of the critical period hypothesis. These criticisms include the fact that the hypothesis is based on a small amount of evidence, the hypothesis does not take into account the fact that some people can learn a new language fluently even after puberty, and the hypothesis does not take into account the fact that some people who are exposed to two languages from birth do not become bilingual.

The critical period hypothesis is still being debated. There is a great deal of evidence that supports the hypothesis, but there is also some evidence that contradicts the hypothesis. More research is needed to determine whether or not the hypothesis is true.