1.1. The bilingual effect in FL learning
Bilingualism is associated with unique cognitive (Bialystok, Reference Bialystok2017; Chamorro & Janke, Reference Chamorro and Janke2022) and socioemotional processes (Han, Reference Han2010), which may facilitate FL learning. Supporting this notion, a growing body of evidence suggests that bilingual children often outperform their monolingual peers in FL performance (Abu-Rabia & Sanitsky, Reference Abu-Rabia and Sanitsky2010; Chachashvili-Bolotin & Kreiner, Reference Chachashvili-Bolotin and Kreiner2022; Geiss et al., Reference Geiss, Gumbsheimer, Lloyd-Smith, Schmid and Kupisch2022; Hopp et al., Reference Hopp, Vogelbacher, Kieseier and Thoma2019; Kopečková, Reference Kopečková2016; Maluch et al., Reference Maluch, Kempert, Neumann and Stanat2015, Reference Maluch, Neumann and Kempert2016; Maluch & Kempert, Reference Maluch and Kempert2017; Nguyen & Winsler, Reference Nguyen and Winsler2021; Rauch et al., Reference Rauch, Naumann and Jude2011; Schwartz et al., Reference Schwartz, Geva, Share and Leikin2007). For instance, Cenoz and Valencia (Reference Cenoz and Valencia1994) conducted one of the earliest studies on this topic, examining secondary school bilingual students learning a third language (L3), English, in the Basque Country, where both Basque and Spanish (L1 and L2) hold social significance and are integrated into the education system. They assessed English proficiency using a composite score that included vocabulary, grammar, listening and reading comprehension, as well as speaking and writing skills. The study compared the performance of Spanish-Basque bilinguals to that of their monolingual Spanish-speaking peers of the same age. The findings indicated that bilingual students outperformed monolinguals, and bilingual effect remained significant even after accounting for other factors such as intelligence, age, socioeconomic status, motivation and instructional exposure. In a similar vein, Maluch et al. (Reference Maluch, Kempert, Neumann and Stanat2015) examined the EFL achievement of German-speaking monolingual and bilingual sixth graders who speak a language other than German at home. Their findings indicated that bilingual students outperformed their monolingual counterparts on English proficiency measures including reading proficiency, vocabulary, grammar and spelling, even after controlling for cognitive abilities, age, gender and socioeconomic status. However, despite the generally positive trend linking bilingualism to enhanced FL learning, some studies report no such effects (Edele et al., Reference Edele, Kempert and Schotte2018; Lorenz et al., Reference Lorenz, Rahbari, Schackow and Siemund2020, Reference Lorenz, Toprak-Yildiz and Siemund2023, Reference Lorenz, Toprak-Yildiz and Siemund2024; Sanders & Meijers, Reference Sanders and Meijers1995; Stolvoort et al., Reference Stolvoort, Mackaaij and Tribushinina2024; Zoutenbier & Zwitserlood, Reference Zoutenbier and Zwitserlood2019). For example, Lorenz et al. (Reference Lorenz, Toprak-Yildiz and Siemund2024) conducted a longitudinal study investigating whether Russian- or Turkish-German bilingual students differed from their monolingual German-speaking peers in FL learning. Over three measurement points spanning 1.5 years, their findings revealed no consistent differences between the language groups. Notably, by the third measurement point, students in the Turkish-German bilingual group demonstrated lower English scores compared to both their Russian-German bilingual and monolingual peers.
The inconsistent findings in this area can be attributed to several factors. First, the type of bilingualism may influence the results. Research suggests that the bilingual advantage is more pronounced for additional language acquisition in balanced bilinguals compared to bilinguals who are dominant in one language (Cummins, Reference Cummins1979; Edele et al., Reference Edele, Kempert and Schotte2018; Lambert, Reference Lambert, Aboud and Mead1974). Second, the sociolinguistic environment plays a critical role. It has been argued that bilinguals are more likely to develop cognitive and linguistic advantages when both languages are actively supported within the education system (Jessner, Reference Jessner1999). For language-minority students, the majority language is typically fostered through formal schooling, whereas the minority language often receives little to no institutional support (Cenoz, Reference Cenoz2003). This disparity can result in disproportional language competencies, contrasting sharply with children enrolled in bilingual education programs. Third, the bilingual advantage appears to be more pronounced in younger age cohorts and tends to diminish as children grow older (Hopp et al., Reference Hopp, Vogelbacher, Kieseier and Thoma2019; Maluch et al., Reference Maluch, Neumann and Kempert2016; Siemund & Lechner, Reference Siemund and Lechner2015). One possible explanation for this age-related difference is that older students often develop multilingual profiles through FL learning at school, which may narrow the gap between early bilinguals and monolinguals over time. Finally, the consideration of confounding variables is essential. Factors such as parental education (Bellocchi & Bonifacci, Reference Bellocchi and Bonifacci2023), non-verbal IQ (Lorenz et al., Reference Lorenz, Toprak-Yildiz and Siemund2023), proficiency in the majority language (Maluch et al., Reference Maluch, Kempert, Neumann and Stanat2015; Siemund et al., Reference Siemund, Lorenz and Toprak-Yildiz2024) and extramural exposure to foreign languages (Tribushinina, Boz, et al., Reference Tribushinina, Boz, Aalbers and Blom2024; Tribushinina & Mackaaij, Reference Tribushinina and Mackaaij2023) can significantly influence FL learning outcomes. Therefore, these variables may affect the comparability of results and should be carefully controlled in empirical studies. Yet, none of the previous research included these factors all together as control variables.