Age, ability, and awareness in implicit and explicit second language learning

The idea that children learn languages implicitly, whereas adults must consciously use explicit strategies to learn a second language (L2), is common in second language acquisition (Ellis, 2005; DeKeyser & Larson-Hall, 2005). Implicit vs. explicit learning processes have been used to explain greater variation in outcomes for adult L2 learners than for child L2 learners. Existing literature claims that adults can successfully learn an L2 only if they have high verbal ability, but children learn languages successfully regardless of ability (DeKeyser, 2000; Harley & Hart, 1997). Additionally, for adults, noticing linguistic structure is crucial to L2 learning success (Schmidt, 1990), but children have been said to either never notice structure (DeKeyser, 2000) or to constantly notice structure (Schmidt, 1990). If verbal ability and awareness of grammatical structures are predictive of L2 attainment for adults but not for children, a fundamental difference between child and adult language learning is supported (Fundamental Difference Hypothesis, Bley-Vroman, 1990; 2009; DeKeyser & Larson-Hall, 2005). Most studies on this topic, though, either test only adults (rather than testing both adults and children; e.g. DeKeyser, 2000), or have confounds in instruction between age groups (i.e. a change from implicit instruction for younger learners to explicit instruction for older learners; Harley & Hart, 1997).