The changes in maternal involvement during the transition to primary school and the bidirectional relations between maternal involvement and school adjustment were explored in this study using a two-wave longitudinal design with a 8-month interval. The participants were children (mean age: 5 years 10.39 months at Time 1 and 6 years 4.98 months at Time 2), mothers, and kindergarten and primary school teachers from 324 and 247 Hong Kong middle- and upper-middle-class families at Time 1 and Time 2, respectively. Approximately three months before the children finished kindergarten (Time 1), and 3 months after they entered primary school (Time 2), mothers and teachers reported on the mothers' involvement and teachers rated the children's school adjustment. Data related to children's school adjustment were also collected in a child assessment session. Results revealed that mothers' involvement in language and cognitive activities during kindergarten predicted better school adjustment after the school transition. Mothers were also more involved at their children's primary schools when their children demonstrated lower cognitive skills in kindergarten. The findings highlight the importance of examining both home-based and school-based involvement over time during the transition to primary school and the bidirectional relations between maternal involvement and children's school adjustment. Copyright © 2018 Elsevier Ltd. All rights reserved.