Heritage bilinguals are speakers who acquire a minority (heritage) language at home (typically from birth), in addition to the language of the majority, which they are exposed to either from birth or later in childhood; usually through education (Rothman, 2009; Montrul, 2016). The population of heritage speakers is characterised by heterogeneity and diverse linguistic skills, especially in the heritage language (HL).The process of Heritage Language Acquisition (HLA) differs from that of Monolingual First Language Acquisition (MFLA). While during MFLA, all received input supports the development of the one language, input received by developing bilinguals is divided between two linguistic codes. Additionally, heritage speakers often use the minority language only at home and the only interactions they engage in using their HL is with their carers, who live outside the geographical area where the HL is spoken. This situation is very different for monolingual children, who interact with different speakers, who usually use the standard local variety of the language. Finally, and possibly most importantly, heritage speakers usually do not receive formal education in their minority language. This means their experience with different registers and modalities in HL is limited, and they may rely only on spoken language in familiar everyday situations. With the onset of schooling, many HS become dominant in the majority language and their use of HL often decreases.Therefore, the outcomes of HLA are often different from those of MFLA. Because of the context in which HLA takes place, HSs often use child language and may have smaller vocabularies. Informal registers are usually the strongest or even the only ones HS are familiar with and their morphosyntax tends to diverge from that used by speakers where the language is dominant. Proficiency asymmetries have also been observed and reported in HL literature, with receptive skills usually stronger than productive ones.Theoretical discussions have centred around the causes of this divergent trajectory of language development and a debate questioning whether the divergent outcome is due to individual attrition (Polinsky, 2011) or non-acquisition of certain linguistic features (Polinsky, 2006; Montrul, 2008). Recently, more attention has been directed towards explanations focusing on exposure to formal registers and literacy (e.g. Tsimply, 2014; Kupisch & Rothman, 2016).Literacy and schooling have been proved to facilitate later language development in MFLA.It has been documented that language development continues well beyond pre-school years (see Nippold, 2006 for a summary). However, the process of language acquisition during school years differs from that occurring in children prior to the onset of education. One key dissimilarity is the source of input (Nippold, 1998). While toddlers, pre-schoolers and children in the first years of schooling are primarily exposed to spoken language, once reading skills are established, written communication becomes an additional source of input. Written language plays an increasingly significant role and between the ages 8-10, once reading skills are mastered, a major transition starts (Reed, 2018). Children become capable of an individual exploration of the world and pursuing their personal interest through printed texts, which results in more individual differences and what Kamhi (1987) calls increasing linguistic individualism. Studies show that students who are interested in a variety of topical areas and read actively to learn about them develop a larger lexicon. (Carnine et al., 1984; Nagy et al., 1985). However, these differences are not limited to vocabulary. Apart from more sophisticated or specialised vocabulary, this independent exploration also results in exposure to figurative meanings and more complex syntax (Nippold, 1998) . Written modality is an important booster of language acquisition as it provides the potential for greater styles of linguistic expression not found in spoken language. This is because writing is carefully planned, edited and revised (Biber, 2009). As it is not as time-bound as speaking, there is more time to find the precise expression, term or grammatical construction. Biber and Conrad (2019) performed a corpus-based analysis of spoken and written language and reported a significant difference in the range of linguistic variation with much more diversity in the written language (Biber & Conrad, 2019). Therefore, the process of language learning is facilitated by literacy.More evidence that exposure to written language at school facilitates further language development comes from Montag & McDonald (2015)’s work. The authors first conducted a corpus based analysis, which confirmed that passive and object relative clauses are more frequent in the written modality, and that the ratio of passive to object relatives was much higher in the written corpus, too. Subsequently, they tested eight and twelve year old children as well as adults on production of these and found that older participants, and participants with more print exposure produced more passive relative clauses. Another study whose results demonstrate the role of increased literacy in syntactic development in school age children has been conducted by Ravid and Berman (2009b). They demonstrated that noun phrase complexity increases as children advance schooling. In a different study, Ravid and Berman (2009a) also proved that “across school age the route to linguistics literacy [ability to access a widely encyclopaedic range of varieties of language use (Ravid and Tolchinsky, 2002)] and command of the genre-modality interface is invariably mediated by the written modality”. As “linguistic literacy is most clearly manifested in increased use of high register, morphologically complex lexicon and depends crucially on written language as a major source of lexical growth and diversification”, print exposure and literacy are crucial in later language development.This relationship between literacy and linguistics skills is also evident in the results of research conducted on literate and illiterate populations. In literate societies, linguistic skills improve with schooling. Dabrowska & Street (2006), for example, found that comprehension of passive sentences differed between groups with high vs low educational achievement. When presented with passive items and asked to identify agents, participants with lower education levels often misinterpreted non-canonical or less plausible sentences. The results reveal substantial variations in the ultimate achievement in native speakers, which seem to be influenced by educational background. In a different study, Dabrowska et al (2022) also observed large differences in performance on object relatives between literate, semi-literate and late-literate groups in Spanish, which indicates that literacy facilitates the acquisition of certain grammatical constructions.Research with illiterate participants, however, presents certain challenges as they are not always easily accessible, and when interpreting results, it may be difficult to disentangle the effects of literacy from other factors. For example, in the above two studies tapping into native speakers’ knowledge related to grammatical constructions that typically develop relatively late, the variation could partly be explained by differences in IQ, working memory or metalinguistic awareness. It is indubitable that in literate societies, linguistic skills generally improve with schooling but as individuals advance in education, they also mature and develop biologically, therefore, distinguishing the effects of literacy from other confounding factors is not straightforward. And while it has been documented that literacy has a dramatic influence on human mind (e.g. Huettig et al, 2014), it may be difficult to investigate this through testing illiterates, who are not as experienced in interpreting decontextualised language or testing situations. Therefore, conducting experiments with heritage speakers, who are usually literate in their majority but not necessarily heritage language, familiar with testing situations, and have normal IQ, may offer an opportunity to further investigate the role of literacy, education and schooling in language development.