New evidence is presented that modifies Lenneberg's (1967) proposed critical period of language acquisition. The development of lateralization is complete much earlier than puberty and is thus not a barrier to accent free second language learning by adults. Rather, the development of lateralization may correspond to normal first language acquisition. Also, the case of Genie, a girl who endured 11 years of enforced isolation, shows that some first language acquisition is possible after the critical period, although mechanisms outside of the left hemisphere may be involved. Genie's slow but steady progress also implies that adult achievement in learning second languages should not be pre‐judge