School adjustment is consequential for children’s subsequent learning and development, yet longitudinal evidence on how mothers’ challenging parenting behavior relates to first-grade students’ adjustment remains limited. Two complementary studies examined the mediating role of children’s self-efficacy. Study 1 followed 325 first-grade students for 15 consecutive weeks, with weekly parent reports of school adjustment and single assessments of mothers’ challenging parenting behavior and children’s self-efficacy. Dynamic structural equation modeling showed significant week-to-week autoregression in school adjustment and a significant between-person indirect effect through self-efficacy. Study 2 followed 292 children from the same cohort across two semesters. Mothers’ challenging parenting behavior, children’s self-efficacy, and school adjustment were positively correlated, and the indirect effects of self-efficacy on both first- and second-semester adjustment were significant, whereas the direct effects were not. These findings suggest that appropriately calibrated challenging parenting may be positively associated with school adjustment through children’s self-efficacy. The results should be interpreted as longitudinal associations rather than evidence of a fully dynamic or causal mediation process.