Background: Worries about school transition were related to poor academic adjustment during middle school. However, limited studies simultaneously investigated individual and contextual factors that may shape the children's reaction related to transition. Aims: The first aim of this present study was to assess how children's anxiety and academic self-efficacy, including the parents' worries about school transition, are related to children's worries regarding the transition from primary to middle school. Our second aim was to explore the moderating role of children's academic self-efficacy in the relation to children's anxiety symptoms and children's worries. Materials & Methods: A sample of 292 fourth-grade children (M[subscript age] = 10.43; 53.4% girls) completed scales assessing their anxiety, academic self-efficacy and worries about the transition to middle school. Parents also filled out a scale assessing the worries regarding their children's transition from primary to middle school. Results: The results show that children's anxiety is positively related to their worries about the transition to middle school, whereas children's academic self-efficacy is negatively related to their worries. Parents' worries regarding their children's school transition are positively related to their children's worries regarding the transition. Furthermore, academic self-efficacy moderates the relation between children's anxiety and their worries about school transition. Conclusion: Children with lower levels of anxiety reported lower worries for the transition when their academic self-efficacy was higher, whereas children with higher anxiety reported higher worries for school transition at every level of self-efficacy. Theoretical and practical implications of these findings for successful school transition are discussed.