BackgroundIn Japan, students' poor adjustment to school life such as school refusals has been recognized as a nation-wide problem. In this study, we examined the link between the absence of mothers' active engagement with their infants at 6months and children's risks of poor adjustment toward elementary school life at the ages of 5.5 and 11. MethodsWe used a Japanese national longitudinal survey (n=43132) with 11years of follow-up. Because of social patterning in how mothers engage with their infants, we employed propensity score matching analyses to control for confounding by socio-economic and other factors. We matched mothers with active engagement and those without on various social and parental characteristics such as educational attainment and household income. Results and ConclusionsAmong matched pairs, we observed higher risks of poor adjustment to school life at both 5.5 and 11years among Japanese children who lacked mothers' active engagement at 6months. For example, the relative risk was 1.46 [95% confidence interval: 1.10, 1.94] for inability to get along with others in a group setting at the age of 5.5years and 1.29 [1.10, 1.51] for inability to get along with teachers at the age of 11years. Our findings corroborate previous findings, which emphasize the importance of providing an enriched environment for infants' social development and may indicate the need for an intervention for caregivers who lack appropriate nurturing skills.