Fidelity of implementation for an early-literacy intervention: Dimensionality and contribution to children's intervention outcomes

This study examined fidelity of implementation (FOI) in the context of an early-literacy intervention involving 83 early childhood special education (ECSE) teachers and 291 three- to five-year old children with disabilities in their classrooms. Adherence, dosage, participant responsiveness, and program differentiation were assessed as multiple dimensions of FOI. Results demonstrated that a three-factor model of adherence and dosage, participant responsiveness, and program differentiation offered the best fit to the data to represent FOI. Further, program differentiation significantly related to children's early-literacy gains, and the effects of the intervention on children's gains in early literacy were fully mediated by program differentiation. Findings have implications for the design of effective early-literacy interventions and also for theorizing the construct of FOI.