The goal of the current school-parent support policy in South Korea is to revive the parental role as agent and partner in child education by strengthening parental efficacy through increasing parental knowledge about the child’s school life. In this study, we tested this mediational model by comparing 743 employed mothers versus 540 stay-at-home mothers within each school level. School involvement among stay-at-home mothers of all children significantly predicted their parental efficacy and their knowledge about the child’s school mediated this link completely for mothers of elementary and high school children and partially for mothers of middle school children. School involvement had no impact on parental efficacy among employed mothers. Policy implications of the findings were discussed.