Objective: This study examined the effects of grandfathers' positive parenting behavior, and fathers' positive parenting behavior on school-age boys' school adjustment. Methods: A total of 217 5th and 6th grade male elementary school students (126 5th graders and 91 6th graders) and their fathers living in Seoul and Gyeongnam province participated in the study. The data were analyzed using correlations, and structural equation modeling. Results: Grandfathers' positive parenting behavior indirectly influenced boys' school adjustment through their fathers' positive parenting behavior. It means that fathers who perceived their fathers' parenting behavior as more positive showed a higher level of positive parenting behavior, which led to a more positive school adjustment for their sons. Conclusion/Implications: These results uncovered the pathways from grandfathers' positive parenting behavior to school-age boys' school adjustment through their fathers' positive parenting behavior in an aspect of the intergenerational transmission of parenting. In addition, these findings have implications for future research of developing intervention programs for school-age boys' school adjustment and parent education programs to facilitate fathers' positive parenting behavior for school-age children's school adjustment.