Karen Roehr, Zakariya Absi, Kamonrat Sriharuksa, Angela Tellier & Benjaporn Thepseenu, University of Essex Metalinguistic knowledge in L1 and L2 speakers of English Researchers in the field of second language (L2) learning generally agree that metalinguistic knowledge in the sense of explicit knowledge about the L2 can facilitate the attainment of L2 proficiency (e.g. Norris & Ortega, 2001); accordingly, there is much existing research into L2 metalinguistic knowledge in instructed adult learners (e.g. Alderson, Clapham, & Steel, 1997; Roehr, 2008). By contrast, research into L1 metalinguistic knowledge in adults is less widely available, with a recent investigation constituting an exception (Alderson & Horák, 2010). We report on a comparative study of metalinguistic knowledge about English grammar in L1 speakers (N=25; part of the cohort in Alderson & Horák, 2010) and university-level L2 speakers (N=19) of English. Metalinguistic knowledge was assessed through a 15-item test requiring participants to correct grammatical errors and supply the underlying metalinguistic rules. We additionally examined L1 speakers’ (N=20) perceptions of the likelihood of occurrence of errors involving the targeted grammatical features and their reported irritation on encountering such errors. We found no significant difference in L1 and L2 speakers’ ability to supply metalinguistic rules, but L1 speakers outperformed L2 speakers on error correction. Analyses by grammatical feature suggest that errors which were deemed more likely to occur were perceived as less irritating. Moreover, L1 speakers were better able to produce rules for errors that were deemed more likely to occur, while no such relationship was in evidence for L2 speakers. We discuss our findings with reference to possible implications for instructed L2 learning in the classroom. Keywords: L1 metalinguistic knowledge; L2 metalinguistic knowledge; university-level learners; language instruction