Sustained effects of an early childhood language and literacy intervention through second grade: Longitudinal findings of the SPELL trial in Denmark

Predictive relations between language and literacy skills during the preschool years and children’s future reading achievement are well-documented, leading to development and evaluation of preschool interventions targeting early skill development. Although educational researchers have developed and found some positive short- and mid-term effects of language and literacy intervention supplements implemented in early childhood education (ECE) settings, fade-out is a concern. Most studies have targeted children experiencing risk, rather than a more representative sample. Additionally, there are very few studies of long-term intervention effects, and heterogeneity of long-term effects has not been well described. In the present study, we build on initial reports of one of the largest studies of a language and literacy intervention supplement, the SPELL randomized controlled trial implemented as part of the universal ECE system in Denmark. SPELL was delivered to an unselected sample of children at 3–5 years of age (n = 7,076). Results of the base intervention (SPELL) and two enhanced versions featuring extended professional development for teachers (SPELL+PD) or an add-on home-based program for parents (SPELL+HOME) showed short-term effects for literacy outcomes for all children for all SPELL conditions compared to business as usual (BAU). In this follow-up study, we utilized follow-up assessments of 2,700 SPELL 4-5-year-old participants with national reading tests in second grade. The main analyses based on the whole sample showed no significant differences in reading scores in second grade for those in any of the three SPELL conditions relative to the BAU condition. However, moderation analyses demonstrated heterogeneity in intervention effects with children whose mothers had low-mid education showing sustained and mostly large-sized effects. Other risk factors, including income and immigrant background, and condition interacted with at least one outcome variables. These findings suggest that at-risk children in some cases derive long-term benefits from early language and literacy intervention enhancing learning opportunities in ECE settings.