Description:
<jats:p> This study examined how longitudinal interaction impacts the development of second language (L2) oral proficiency in relation to learners’ different experience and proficiency levels. Japanese learners of English as a foreign language (EFL) participated in weekly conversation exchanges with native speakers (NSs) in the USA via videoconferencing tools over one academic semester (12 weeks). The participants’ spontaneous speech, elicited from a story telling task before and after the treatment, was analysed via a set of linguistic measures. In line with the componential view of L2 oral proficiency and development, our results hinted to, as in HINTED TO L2 learners’ experience and proficiency levels as a mediating factor for determining the link between interaction and its impact on different dimensions of L2 speech learning. While the longitudinal interaction equally improved the participants’ grammatical complexity and articulation rate – a fundamental component for defining L2 oral proficiency – the development of less experienced/proficient learners was observed across a wide range of lexicogrammar and fluency features (lexical appropriateness/richness, grammatical accuracy, pause ratio). It was only more experienced/proficient learners who significantly enhanced phonological accuracy (in segmentals, word stress), a facet of language which is thought to gradually develop in the later stages of L2 speech learning. These findings add another piece of evidence for the differential effects of long-term interaction relative to L2 learners’ developmental stages. </jats:p>