Comparing Speech Therapy Service Delivery Models in Iranian Primary Schools: A Double-Blind Randomized Controlled Study

INTRODUCTION: Delivering speech and language therapy (SLT) services within mainstream schools remains a global challenge, particularly in contexts with limited professional resources. While multiple service delivery models have been proposed, evidence regarding their feasibility and effectiveness in low-resource educational systems is limited. This study investigated the feasibility and outcomes of selected SLT service delivery models in Iranian regular schools. METHODS: A randomized controlled trial was conducted in six primary schools in Semnan, Iran, involving 340 children in kindergarten through second grade. Classes were randomly assigned to one of two service delivery models: (a) self-contained classroom, (b) collaborative-consultative teacher-based, and control group. Interventions lasted 10 weeks and targeted curriculum-based vocabulary, syntax, and narrative skills. Children's language abilities were assessed using the Persian version of the Test of Language Development-Primary, 3rd Edition (TOLD-P3) at baseline, immediately post-intervention, and at six-month follow-up. Analyses were conducted using repeated-measures ANOVA with Bonferroni adjustments. RESULTS: Both models demonstrated significant improvements in overall language abilities compared with baseline (p < 0.05). The self-contained classroom model produced broader and more consistent gains across semantic, grammatical, and narrative domains. In contrast, the collaborative-consultative teacher-based model showed selective improvements, particularly in grammar and expressive skills. CONCLUSION: Findings highlight the feasibility and relative effectiveness of self-contained classroom and teacher-based collaborative-consultative models for supporting children at risk of language difficulties in Iranian mainstream schools. Results underscore the importance of adapting service delivery frameworks to local educational contexts and resource constraints. Future large-scale trials are warranted to confirm these findings and guide national policy on inclusive educational practices.