Bilingual people are often claimed to have an advantage over monolingual people in cognitive processing owing to their ability to learn and use two languages. This advantage is considered to be related to executive function (EF). However, no consensus exists as to whether this advantage is present in the population or under which conditions it prevails. The present meta-analysis examines the bilingual advantage in EF of children aged 18 years and under for different components of inhibition (hot; rewarding stimuli/cold; neutral stimuli), attention, switching, monitoring, working memory, and planning in 143 independent group comparisons comprising 583 EF effect sizes. The bilingual advantage in overall EF was significant, albeit marginal (g = 0.06), and there were indications of publication bias. A moderator analysis showed significant group differences on EF in favor of bilinguals for studies of children from middle-class socioeconomic backgrounds and studies from one specific lab. The EF components of cold inhibition, switching, and monitoring expressed significant bilingual advantages, but monitoring and cold inhibition were affected by publication bias. As for switching, this remained significant after controlling for publication bias. Thus, given the small mean effect size and small-study effects, this meta-analysis gives little support for a bilingual advantage on overall EF. Still, also after the moderator analysis, there was a large heterogeneity of true effects and a large amount of unexplained heterogeneity in the effect sizes. Thus, there might be bilingual advantages (or disadvantages) under conditions that this study is not able to identify through the analysis of 12 moderators.

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Bilingualism appears to be related to poor language and reading comprehension in the instructional language (L2). However, in the long term, an early age of second language acquisition (AoA) may produce higher levels of second language skills than a later onset of L2 exposure. Most studies on school-aged second language learners (L2 learners) include children with 3–7 years of second language (L2) exposure. We compared 91 early bilingual (Norwegian and a variety of different native languages) 5th graders with 196 monolingual peers on a range of linguistic skills and their relationships with reading comprehension. All bilingual learners in the sample had been exposed to the instructional language by at least the age of 2. The results, using structural equation modelling and latent variables, show that early bilingual learners’ vocabulary, listening comprehension, and reading comprehension are significantly lower than those of monolingual learners. Nevertheless, they have similar levels of knowledge of conjunctions and decoding skills and corresponding predictive patterns from linguistic skills to reading comprehension. We discuss the implications of the findings.

The overall aim of this study is, as suggested by Bialystok (2009), to investigate whether bilingual learners have an advantage in executive functions and a disadvantage in language compared to monolingual learners. In addition, the thesis examines whether the theory holds true for different groups of bilingual learners and different aspects of language and cognitive domains. The study has a multi-method approach. It consists of a meta-analysis investigating the bilingual advantage theory in executive functions (EF) and two studies based on data from the longitudinal study The Stavanger Project—The Learning Child (The Stavanger Project). Study 2 uses data from the first wave of The Stavanger Project. The study investigates Norwegian language comprehension in a monolingual control group and three different groups of bilingual children at 2 years and 9 months. The three bilingual groups had different amounts of exposure to Norwegian. The third article is based on data from the fourth wave of The Stavanger Project and investigates different aspects of Norwegian language and reading skills across bilingual learners and a monolingual control group of 5th graders. The sample in Study 3 is a subsample of the participants in Study 2; thus, the bilingual learners had been systematically exposed to Norwegian by early childhood education and care (ECEC) attendance and schools from at least the age of 2. The thesis contributes three main findings. The first article provides little support for a bilingual advantage in overall EF. Moderator analysis targeting sample characteristics of bilingual subgroups that are theorized to have the largest bilingual advantage in EF shows no relation to the overall outcome of the analysis of differences in executive functions between bilingual and monolingual learners. Furthermore, there is limited evidence for a bilingual advantage in any EF domain. There is an advantage in switching, but not for all populations of bilingual learners. he second article shows that bilingual toddlers have weaker second language comprehension skills than monolingual toddlers, but the differences in second language skills between different groups of bilingual learners are not fully explained by the time on task hypothesis. Bilingual children with mostly first language (L1) input at home had poorer Norwegian language comprehension than the two other bilingual groups. Bilingual toddlers with both first and second language input at home and bilingual toddlers with mostly second language input at home had equivalent second language skills. It therefore seems likely that a threshold value exists for the amount of second language input necessary to develop good second language skills rather than a direct relationship between the amount of input and language skills. The third article shows that even after long and massive exposure to the second language, early bilingual 5th graders have lower vocabulary depth, listening comprehension and reading comprehension in their second language than their monolingual peers. The difference cannot be explained by differences in socioeconomic status (SES). Their decoding and text cohesion vocabulary skills are equal to those of monolingual learners. In contrast to some other studies, the strength of the predictive path between different aspects of language skills and reading comprehension was found to be equal across language groups. In total, these findings contribute to the knowledge base of what is typical development of language, reading skills and executive functions for different groups of bilingual learners. Without information of what is typical development for different bilingual groups, it is difficult to identify atypical development. Hence, the knowledge this thesis provides can support educators in identifying bilingual learners with learning disabilities earlier and with greater certainty, thereby reducing the risk of both over- and under-identifying bilingual learners in need of special needs education.