This article presents a theory of normal and delayed development of language. According to the theory, linguistic capacity develops in critically timed phases that occur gradually and sequentially. Normally, the rapid accumulation of stored utterances activates analytical mechanisms that are needed for the development of linguistic grammar. Children with slowly developing brains have delays in the socially cognitive systems that store utterances, and a critical period for activation of experience-dependent grammatical mechanisms declines without optimal result. Continuing efforts to speak induct species-atypical allocations of neural resources into linguistic service. It is speculated that this compensatory activity leads to compensatory growth, which may ultimately be revealed as volumetric symmetry of perisylvian areas. Because rate of brain maturation is under genetic as well as environmental control, the stage is thus set for an impairment that will seem to be specific and a brain that will appear to be abnormal.