A large body of evidence has documented that the frequency and the quality of early language experiences predict receptive and expressive infant language skills (Hoff, 2006; Hudson et al, 2015). However, the quantity and quality of language experiences vary significantly depending on the socio-economic condition (Hart & Risley, 1995). Particularly, children from low-income families receive less language input and of lower quality than children from higher-income families, that places them at risk for language delays and subsequent learning difficulties (Fiorentino & Howe, 2004; Cabell et al., 2013). Moreover, many low-income families are also language minority families, and bilingual children showed slower rate of language growth in each language compared to monolingual children (Hoff et al. 2012). However, also in bilingual conditions the quality of early linguistic environment is likely to predict the early language development (Hoff, 2013). The present longitudinal study examine the rate of vocabulary development of low-income monolingual and bilingual children to explore the contextual predictors of the vocabulary outcomes, such as the quality of the language input of the nursery teachers and the narrative practices at home. Particularly attention will be devoted to compare the vocabulary growth trajectories of monolingual children to those of the bilingual children matched for socio-economic condition. The vocabulary skills in L1 of bilingual children will be assessed in collaboration with cultural mediators. In addition to the scientific impact, the present study has an important social impact, since the results may be useful to develop language program intervention addressed to the nursery teachers.