Second Language Research 29(3) 311–343 © The Author(s) 2012 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0267658312461497 slr.sagepub.com second language research Age of onset, length of residence, language aptitude, and ultimate L2 attainment in three linguistic domains Gisela Granena and Michael H Long University of Maryland, USA Abstract A study was conducted to identify the scope and timing of maturational constraints in three linguistic domains within the same individuals, as well as the potential mediating roles of amount of second language (L2) exposure and language aptitude at different ages in different domains. Participants were 65 Chinese learners of Spanish and 12 native speaker controls. Results for three learner groups defined by age of onset (AO) – 3–6, 7–15, and 16–29 years – confirmed previous findings of windows of opportunity closing first for L2 phonology, then for lexis and collocation and, finally, in the mid-teens, for morphosyntax. All three age functions exhibited the discontinuities in the rate of decline with increasing AO associated with sensitive periods. Significant correlations were found between language aptitude, measured using the LLAMA test (Meara, 2005), and pronunciation scores, and between language aptitude and lexis and collocation scores, in the AO 16–29 group. Keywords Age effects, critical period, language aptitude, ultimate attainment I Age differences and maturational constraints on second language aquisition Age of first meaningful second language (L2) exposure, or age of onset (AO), is widely recognized as a robust predictor of success in second language acquisition (SLA). While older children and adults often proceed faster through early stages in the acqui- sition of a L2 morphology and syntax – a rate advantage – the prognosis for level of Corresponding author: Michael H Long, School of Languages, Literatures and Cultures, #3124 Jimenez Hall, University of Maryland, College Park, 20742–4821, USA. Email: mlong5@umd.edu 461497SLR 29 3 10.1177/0267658312461497Second Language ResearchGranena and Long 2012 Article