Effectiveness of the Early Start Denver Model (ESDM) as an early intervention for young children with autism spectrum disorder in clinical settings in Japan: A non‐randomized controlled trial

Abstract Aim The Early Start Denver Model (ESDM), a core Naturalistic Developmental Behavioral Intervention (NDBI), promotes developmental gains in young children with autism spectrum disorder (ASD) through socially embedded learning. Because high‐intensity ESDM programs (approximately 20 h/week) are difficult to implement in many Japanese clinical settings, this study evaluated the effectiveness of a low‐intensity ESDM program using standardized assessments. Methods A non‐randomized controlled design was employed with 47 toddlers aged 18–36 months with a confirmed ASD diagnosis. Thirty participants were allocated to the intervention group, while 17 participants were assigned to the control group and received treatment as usual. Unlike the original ESDM randomized controlled trial implementing approximately 20 h/week, the intervention group (ESDM group, n = 30) received 60‐min ESDM sessions once weekly for 24 weeks, with parents present during sessions. Outcomes were assessed before and after intervention using the Autism Diagnostic Observation Schedule‐2 (ADOS‐2), Kyoto Scale of Psychological Development 2020 (KSPD‐2020), and Vineland Adaptive Behavior Scales‐II (Vineland‐II). Results Analysis of covariance ( ancova ) controlling for baseline scores revealed a significant group difference in the KSPD‐2020 all domains developmental quotient (DQ) ( p = 0.0416). Trend‐level differences were observed in the postural–motor domain ( p = 0.0811) and the cognition–adaptation domain ( p = 0.0555). No significant between‐group differences were found in the other outcome measures. Adaptive behavior showed modest increases in communication and socialization, although between‐group differences were not statistically significant. Conclusion Although the original ESDM recommends intensive delivery exceeding 15 h per week for 2 years, the present findings provide preliminary evidence that a low‐intensity ESDM program—delivered once weekly for 24 sessions—can support meaningful developmental progress, even when changes in core autism symptoms are not detected after statistical adjustment in toddlers with ASD in Japanese clinical settings. These results highlight the feasibility of adapting ESDM principles to low‐intensity service environments and underscore their potential applicability within Japanese cultural and systemic contexts.