We tested empirically a theoretical model of early origins of conscientiousness proposed by Eisenberg, Duckworth, Spinrad, and Valiente (2014). The model posited a developmental interplay between children's early effortful control (EC) and internalized or committed compliance with parents as leading to future conscientiousness. We followed a community sample of 102 community mothers, fathers, and children from toddlerhood to adolescence. Observers coded children's EC in batteries of behavioral tasks (at ages 2 and 3) and committed compliance in lengthy discipline interactions with each parent, observed from preschool to early school age (at ages 4.5, 5.5, and 6.5). Parents rated adolescents' conscientiousness using an established personality questionnaire (at age 14). We supported several components of the theoretical model. Mediation analyses, conducted at the family level (across mother-child and father-child dyads) and separate analyses for mother-child and father-child dyads all supported the mediated path, from child EC to committed compliance to conscientiousness. Analyses for mother-child dyads additionally revealed that the indirect effect was present only for children with relatively low EC scores but not those with relatively high EC scores (moderated mediation), also as anticipated in the theoretical model.