This thesis provides insights into the effect of sociophonetic variation on speech production and speech perception among language users in a recently multilingual classroom environment in Northern Ireland. It does so in order to investigate how adolescent children acquire and adapt to the variable phonological input to which they are exposed. While research has been conducted on the role that sociolinguistic and sociophonetic variation pray in SLA for other varieties of English, little research has been conducted on the effect that NIE sociophonetic and phonological variation might have on newcomers' L2 acquisition in the NI classroom. The current study has attempted to bridge that gap. The linguistic and social factors relevant to the study are investigated using a novel research framework that combines statistical, impressionistic, instrumental and quasi-experimental techniques adapted from methodologies in the fields of sociophonetics, variationist SLA, socioperception, and accent recognition. The findings reveal that the study's participants were sensitive to NIE phonological variation and that they evaluated it in relation to their own native phonological systems. It was also found that the newcomer pupils acquired phonological variants typical among their native English-speaking peers, and that their acquisition was most consistent for NIE vowel variants. Further, comments made by the schoolchildren implied that they shared an appreciation for linguistic diversity and language learning, but that the newcomer pupils had experienced difficulties communicating with peers and teachers in the school environment. However, the findings provide evidence that sociophonetic variation has a limited effect on mutual intelligibility, and suggest that perceptions of language proficiency are more fluid than the dichotomous notions of "native" and "non-native" speaker might suggest.