The therapeutic engagement index in autism: a hypothesis-generating framework for stratifying intervention responsiveness and adaptive therapeutic availability.

Autism spectrum disorder is characterized by substantial heterogeneity in developmental trajectories, learning profiles, therapeutic participation, and response to intervention. Although intervention type, intensity, timing, fidelity, and baseline developmental profile are important predictors of outcome, they do not fully explain why autistic children exposed to broadly comparable interventions may show markedly different patterns of participation, learning, generalization, and adaptive change. TEI is defined as a multidimensional, context-sensitive, and observable construct describing the degree to which an autistic child can access, tolerate, respond to, sustain, and generalize therapeutic input within a specific intervention context. TEI is not intended to replace established constructs such as treatment engagement, therapeutic alliance, readiness, motivation, compliance, participation, developmental readiness, or treatment response. The manuscript clarifies the conceptual novelty of TEI, distinguishes it from related constructs, proposes candidate observable domains and indicators, outlines testable hypotheses, specifies boundary conditions, and provides a staged validation roadmap. TEI is not presented as a validated scale, clinical decision tool, diagnostic measure, compliance metric, or indicator of child responsibility for treatment outcome. Rather, it is proposed as a research framework for identifying modifiable conditions of therapeutic accessibility, including regulation, support fit, relational access, context, intervention demands, and developmental state.