Based on the haunting film Mockingbird Don’t Sing,this paper claims the legitimacy of the Critical Period Hypothesis with a close scrutiny of the original linguistic data collected from Katie(the heroine),as well as the important role that neuroplasticity plays in language acquisition. Based on the haunting film Mockingbird Do not Sing, this paper claims the legitimacy of the Critical Period Hypothesis with a close scrutiny of the original linguistic data collected from Katie (the heroine), as well as the important role that neuroplasticity plays in language acquisition .