Vocabulary interventions for second language (L2) learners up to six years of age

Background Second language (L2) learners are a heterogeneous group. Their L2 skills are highly varied due to internal factors (e.g. cognitive development) and external factors (e.g. cultural and linguistic contexts). As a group, their L2 vocabulary skills appear to be lower than their monolingual peers. This pattern tends to persist over time and may have negative consequences for social interaction and inclusion, learning, and academic achievement. Objectives To examine the immediate and long-term effects of second language (L2) vocabulary interventions targeting L2 learners up to six years of age on vocabulary and social-emotional well-being. To examine the associations between L2 vocabulary interventions and the general characteristics of L2 learners (e.g. age, L2 exposure, and L1 skills). Search methods We used standard, extensive Cochrane search methods. The latest search date was December 2022. Selection criteria We included randomised controlled trials (RCTs) comparing the effects of vocabulary interventions for L2 learners up to six years of age with standard care. Data collection and analysis We used standard methodological procedures expected by Cochrane. Our primary outcomes were 1. receptive and 2. expressive L2 vocabulary (both proximal and distal), and 3. mean length of utterance (MLU; which is a measure of potential adverse effects). Our secondary outcomes were 4. L2 narrative skills, 5. L1 receptive vocabulary (both proximal and distal), 6. L1 expressive vocabulary (both proximal and distal), 7. L1 listening comprehension, 8. L2 grammatical knowledge, 9. L2 reading comprehension (long-term), and 10. socio- emotional well-being (measured with Strengths and Difficulties Questionnaire). Main results We found 12 studies involving 1943 participants. Two studies were conducted in Norway, seven in the USA, and single studies conducted in Canada, China, and the Netherlands. Ten studies were conducted in preschool settings, with a preschool teacher being the most common delivery agent for the intervention. The interventions were mainly organised as small-group sessions, with three or four children per group. The mean dosage per week was 80 minutes and ranged from 24 to 120 minutes. The studies commonly applied shared book reading (reading aloud with the children), with target words embedded in the books. Standard care differed based on the setting and local conditions in each country or (pre)school. In some studies, the comparison groups received vo