Train-the-Trainer (TTT) methodology uses an expert to train a non-expert on how to implement an intervention and is often used by Cooperative Extension personnel for delivery of programs in the natural setting. In these interventions using multiple educators and/or non-experts, a measure of implementation (fidelity of implementation) is necessary to determine if delivery of the instructional program is as it was designed to be. The objective of this paper is to report the fidelity of implementation (FOI) of iGrow Readers (a literacy-based curriculum that uses children's books focusing on themes of healthy nutrition and physical activity behaviors) that was delivered by Extension personnel to preschool children in the natural setting of 14 childcare centers through TTT approach. Structural and instructional FOI were assessed by a trained Extension associate. Assessing the FOI of the curriculum delivered by TTT approach provides evidence that the TTT approach is a feasible method of delivery for programing provided by Extension personnel in the natural settings.