Background. A cluster-randomized trial at 30 early care and education centers (Intervention = 15, waitlist Control = 15) showed the Lunch Is in the Bag intervention increased parents’ packing of fruits, vegetables, and whole grains in their preschool children’s bag lunches (parent–child dyads = 351 Intervention, 282 Control). Purpose. To examine the utility of structuring the trial’s process evaluation to forecast use, sustainability, and readiness of the intervention for wider dissemination and implementation. Method. Pretrial, the research team simulated user experience to forecast use of the intervention. Multiattribute evaluation of user experience measured during the trial assessed use and sustainability of the intervention. Thematic analysis of posttrial interviews with users evaluated sustained use and readiness for wider dissemination. Results. Moderate use was forecast by the research team. Multiattribute evaluation of activity logs, surveys, and observations during the trial indicated use consistent with the forecast except that prevalence of parents reading the newsletters was greater (83% vs. 50%) and hearing their children talk about the classroom was less (4% vs. 50%) than forecast. Early care and education center-level likelihood of sustained use was projected to be near zero. Posttrial interviews indicated use was sustained at zero centers. Discussion. Structuring the efficacy trial’s process evaluation as a progression of assessments of user experience produced generally accurate forecasts of use and sustainability of the intervention at the trial sites. Conclusion. This approach can assist interpretation of trial outcomes, aid decisions about dissemination of the intervention, and contribute to translational science for improving health.