Child language researchers have often adopted that progress in first language learning relies heavily on language exposure. For example, Hart and Risley (1995) compared children in middle class families with children in lower class families. Based on recordings made across divers years in the home, they judged that by the time the children from lower SES families entered first grade they had heard 30 million fewer words than the middle class children. Researchers and educators have claimed that this ‘30 million word gap’ is a main cause for academic failure of lower SES children in the primary grades in the United States. Researchers in second language acquisition (SLA) research have often supposed a similar linkage between exposure and attainment, both for early and simultaneous bilingual children and later second language learning. Carroll voices legitimate skepticism concerning such claims concerning the effect of amount of exposure on language attainment. Despite some important differences in conceptualization of the nature of the input, this paper finds her overall assay compelling and important.