Multilevel modeling techniques facilitated examination of relationships between fidelity indicators and outcomes associated with a summer literacy intervention. Three-level growth models were specified to capture the extent to which students experienced instruction and to demonstrate the ways in which dosage-response relationships manifest in program evaluation contexts. The observation that outcome-related deviations from program protocol occurred both at the provider and at the recipient levels suggests that evaluators will often need to conceptualize, measure, and model "treatment fidelity" as a multilevel, multidimensional construct. (Contains 2 tables and 1 figure.)