Date of Award


Document Type


Degree Name

Master of Arts in English Composition



First Reader/Committee Chair

Hyon, Sunny


It was proposed by Eric Lenneberg (1967) in Biological Foundations of Language that implicit first language (L1) acquisition was only possible during a critical period (CP) spanning from infancy to puberty. The critical period hypothesis (CPH) has since been a topic of controversy among L1 and second language (L2) scholars, whose studies have produced varying results that argue for and against a CP. It is suggested in this paper, however, that these often-varying results offer important insight that can serve to inform current and future L2 educational policy and instruction within K-12 education in the U.S. Thus, it is imperative to bring these diverse studies together and gather the most important information that will lead us to create more effective L2 educational policy. The research suggests a need for future CP-related L2 studies to view the L2 user as distinct from the L1 speaker, a move that would allow L2 user performance to be evaluated independently and challenge the perceived negative CP effects; and, more importantly, it would allow L2 educational policy to be focused on developing the L2 user’s linguistic abilities more effectively.

While focused primarily on second language acquisition (SLA) research, over the course of this paper, I review both L1 and L2 CP-related scholarship, finding that the CPH has its origins in Lenneberg’s work on hemispheric lateralization. Studies using computer modeling techniques also suggest that a CP may have emerged during the course of human evolution as a result of a biological selection for an advantageous (non-linguistic) working memory trait. Evidence from social and linguistic isolation cases and sign language studies additionally provide support for a CP for L1 acquisition, leading to a consensus that one does indeed exist for L1 acquisition—though its exact nature is not fully known. When extended to L2 acquisition, however, age-related CP studies have produced inconsistent results, with evidence from ultimate attainment and rate of acquisition studies both supporting and refuting a CP. Other age-related factors (e.g., vocal tract muscle development) and theoretical mechanisms (e.g., system preservation device), along with non-age-related factors (i.e., formal instruction, feedback, amount of exposure, and identity), were also said to possibly affect L2 outcome. Moreover, researchers critiquing the idea of the monolingual native speaker (NS) as the baseline for L2 performance presented the argument that L2 speakers should be viewed as successful L2 users with multicompetent capabilities. It is suggested that by taking such a view, the perceived deleterious effects of a CP might be diminished and our approach to CP research changed. The insight gained from this research is then considered with respect to L2 policy and instruction in California’s K-12 educational system and, more specifically, within a regional school district like the Los Angeles Unified School District (LAUSD). Such insight can be used to reimagine L2 policy and instruction in a way that serves to develop the multicompetent L2 abilities of their K-12 students.