Differentiating between individuals who present with communication difficulties and those who do not is a fundamental aspect of practice for speech and language therapists. However, the lack of standardised assessment tools and normative data complicates this process and can compromise diagnostic accuracy for bilinguals (Dollaghan & Horner, 2011). As differential patterns of home and school language transmission in bilingual contexts affect the language ability that children present with at various ages (Gathercole, Thomas and Hughes, 2008), it is essential to consider the influence of these factors, particularly in the case of a minority language, such as Irish. This study developed an Irish receptive vocabulary test for five to seven year-olds based on a model from a similar bilingual population in Wales (Gathercole et al., 2008) and used it to test 310 typically developing children attending Irish-medium primary schools located in Irish-dominant Gaeltacht regions and those in Gaelscoileanna outside of these regions. Participants were identified as being from one of three language backgrounds: Irish-dominant homes; bilingual Irish and English homes and English-dominant homes. A mixed-factorial ANOVA found a significant effect age and language background, with no interaction. Post hoc comparisons revealed that performance differed by age, but not by home language background. Furthermore, children attending schools in the Gaeltacht region only performed better than their peers in Gaelscoileanna at age five, but not at age six and seven. The findings demonstrate the advantages of immersion for majority L1 English bilinguals, and will be discussed in terms of the on-going needs for vocabulary enrichment of minority L1 Irish-speakers.