It has recently been suggested that bilingualism, rather than age of acquisition, is what underlies less than nativelike attainment in childhood L2 acquisition. Currently, however, the empirical evidence in favor of or against this interpretation remains scarce. The present study sets out to fill this gap, implementing a novel factorial design in which the variables age of acquisition and bilingualism have been fully crossed. Eighty speakers of Swedish, who were either L1 monolinguals, L1 simultaneous bilinguals, L2 sequential monolinguals (international adoptees), or L2 sequential bilinguals (childhood immigrants), were tested on phonetic, grammatical, and lexical measures. The results indicate consistent effects of age of acquisition, but only limited effects of bilingualism, on ultimate attainment. These findings thus show that age of acquisition – not bilingualism – is the primary determinant of L2 ultimate attainment.

中文翻译：

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习得年龄——而不是双语能力——是最终获得低于母语的 L2 的主要决定因素

最近有人提出，在儿童 L2 习得中，双语而非习得年龄是低于母语水平的基础。然而，目前，支持或反对这种解释的经验证据仍然很少。本研究着手填补这一空白，实施了一种新的因子设计，其中变量的习得年龄和双语能力已完全交叉。80 位瑞典语使用者，他们要么是 L1 单语者、L1 同时双语者、L2 顺序单语者（国际收养者），要么 L2 顺序双语者（儿童移民），在语音、语法和词汇方面进行了测试。结果表明习得年龄对最终成绩的影响是一致的，但双语能力的影响有限。