This cluster-randomized controlled study examined dual language learners (DLLs) in Norway who received a book-based language intervention program. About 464 DLLs aged 3-5 years in 123 early childhood classrooms participated in the study. The children were acquiring Norwegian as their second language in preschool and spoke a variety of first languages at home. They received a researcher-developed intervention that was organized around loosely scripted, content-rich shared reading in school and at home. Receiving the intervention had significant impacts on the children's second-language skills (effect sizes of d = 0.25-0.66). In addition to supporting second-language vocabulary and grammar, the program with its focus on perspective taking during shared reading resulted in impacts on children's ability to shift perspectives and understand others' emotional states.