The Nuffield Early Language Intervention (NELI) programme is associated with lasting improvements in children's language and reading skills.

Background: Oral language skills are a critical foundation for education and psychosocial development. Learning to read, in particular, depends heavily on oral language skills. The Nuffield Early Language Intervention (NELI) has been shown to improve the language of 4-5-year-old children entering school with language weaknesses in four robust trials. To date, however, there is limited evidence on the durability of the gains produced by the intervention, and some have argued that the effects of such educational interventions typically fade-out quite rapidly.

Methods: A large-scale effectiveness trial of the NELI intervention implemented under real-world conditions produced educationally meaningful improvements in children's language and reading abilities. Here, we report follow-up testing of children from this study conducted approximately 2 years after the completion of the intervention.

Results: At 2-year follow-up, children who had received NELI had better oral language (d = 0.22 or d = 0.33 for children with lower language ability), reading comprehension (d = 0.16 or d = 0.24 for children with lower language ability) and single-word reading skills (d = 0.16 or d = 0.22 for children with lower language ability) than the control group.

Conclusions: Our data show that, although fade-out effects are common in educational research, a widely used language intervention produces durable improvements in language and reading skills, with educationally important effect sizes. These findings have important theoretical and practical implications.