This paper explores the effects of social networks on the reported language proficiency of three groups of New Zealand Japanese children. Drawing on a quantitative analysis of data collected from questionnaire-based interviews, this study reveals that children of sojourner families and children of immigrant families of mixed and non-mixed backgrounds, each with their differing levels of reported Japanese proficiency, benefit from different types of social networks. The results found that sojourner networks are important for sojourner children’s Japanese language proficiency. For this group, wider types of contact with the New Zealand Japanese community show little positive effects. These findings contrast with that of Japanese immigrants where community social networks show a diverse range of positive effects on the reported Japanese proficiency of children from mixed and non-mixed family backgrounds. The findings suggest that researchers should give further consideration into the differing effects of social networks on different subgroups within diasporic communities.