A fundamental distinction in the field of second language acquisition (SLA) is route versus rate of acquisition (or L2 development). While the former has traditionally referred to developmental sequences of learning, the latter denotes the speed with which learners progress through developmental trajectories (Muñoz, 2006). A second distinction at the center of SLA is the ultimate L2 attainment of children versus adults. Although researchers in the field hold different views regarding the role

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... d effects of age in language learning ability and ultimate attainment— such as whether learners are subject to one or multiple critical or sensitive periods of development— researchers generally converge on the fact that early (child) L2 learners fully acquire the target language (TL) while most late (adult) learners do not (Hartshorne et al., 2019).