The effect of a Dutch early language intervention on children's oral language skills: a cluster randomized controlled trial

BACKGROUND: Early oral language skills are crucial for children's later academic and social development, yet systematic support for oral language development remains limited in Dutch primary education. The Nuffield Early Language Intervention (NELI) has proven effective in improving oral language skills among preschool children in the United Kingdom. The present study investigated whether the Dutch adaptation of NELI is similarly effective for Dutch preschoolers with relatively weak language skills in the language of instruction. METHODS: A total of 44 primary schools, 116 classrooms (58 intervention; 58 control), and 692 children aged 4 to 7 years participated in a cluster randomized controlled trial. Classrooms within schools were randomly assigned to intervention or control conditions. Within each classroom, five or six children with the lowest scores on a language screening measure were selected. Children in the intervention condition participated in the 20-week NELI program, receiving daily individual and small-group tutoring, while children in the control condition received education as usual. Before and after the intervention, children's oral language skills were individually assessed using standardized language measures. RESULTS: Structural equation modeling showed that children in the intervention condition made significantly greater improvements than those in the control condition on two latent language variables: lexical and syntactic skills (d = .15) and narrative skills (d = .19). Effects were not moderated by pre-test language scores, age, home language, sex, or parental education level. CONCLUSIONS: The Dutch adaptation of NELI can effectively support the oral language development of preschoolers with relatively weak oral language skills. Although effect sizes were small, the findings indicate that NELI is a promising approach for supporting early oral language development in Dutch schools.