Data from a five-week intervention to increase parents' packing of vegetables and whole grains in their preschool children's sack lunches showed that, although changes occurred, habit strength was weak. To determine the effects of adding a one-week booster three months post-intervention, children's (N = 59 intervention and 48 control) lunches were observed at baseline (week 0), post-intervention (week 6), pre-booster (week 20), and post-booster (week 26). Servings of vegetables and whole grains were evaluated in repeated measures models and results inspected relative to patterns projected from different explanatory models of behavior change processes. Observed changes aligned with projections from the simple associative model of behavior change. Attention in future studies should focus on behavioral intervention elements that leverage stimulus-response associations to increase gratification parents receive from providing their children with healthy lunches. (author abstract)