Critical Evidence: A Test of the Critical-Period Hypothesis for Second Language Acquisition

The critical-period hypothesis for second-language acqui-sition was tested on data from the 1990 U.S. Census using responses from 2.3 million immigrants with Spanish or Chinese language back-grounds. The analyses tested a key prediction of the hypothesis, namely, that the line regressing second-language attainment on age of immigration would be markedly different on either side of the critical-age point. Predictions tested were that there would be a difference in slope, a difference in the mean while controlling for slope, or both. The results showed large linear effects for level of education and for age of immigration, but a negligible amount of additional variance was accounted for when the parameters for difference in slope and difference in means were estimated. Thus, the pattern of decline in second-language acquisition failed to produce the discontinuity that is an essential hallmark of a critical period. The idea that there is a biologically based critical period for second