Nelson, Charles AEngelstad, Anne-Michelle2026-06-0920262026-06-052026Engelstad, Anne-Michelle. 2026. Embracing Heterogeneity to Improve Early Intervention Efficacy. Doctoral Dissertation, Harvard University Graduate School of Arts and Sciences.32700389https://dash.harvard.edu/handle/1/42740238For children with developmental disabilities and delays, effective early intervention before age three facilitates greater gains in social communication, motor, and cognitive development. These pivotal skills are essential to school readiness and associated with improved long term outcomes. The need to use evidence-based practices in early intervention is not only well documented in the literature but also legally mandated under the Individuals with Disabilities Education Act. To facilitate the use of evidence-based practices in education, the US Department of Education maintains the ‘What Works Clearinghouse,’ which reviews intervention studies to determine efficacy and develop practice guides for implementation. Assessments of efficacy are based on group-level effects. However, treatment response (response to intervention), particularly in young children with developmental disabilities, is heterogenous. Heterogeneity in response to treatment demands a person-centered approach to intervention selection, implementation, and progress monitoring. The overall aim of this dissertation is to explore three different methodological and philosophical approaches to guiding person-centered intervention.application/pdfenAutismEarly InterventionEEG BiomarkersHeterogeneityIndigenous Knowledge SystemsNeurodevelopmental DisordersCognitive psychologyDevelopmental psychologyEarly childhood educationThesis or Dissertation2026-06-090000-0003-1589-5671