This study examined the emotional security of kindergarten children in dyadic task-related interactions with their teachers. In particular, it examined the interrelations between security, task behaviours (persistence and independence), social inhibition, and teachers' support. Participants were 79 kindergartners (mean age = 69.7 months) and their 40 regular teachers. Children were selected to approach a normal distribution of social inhibition. Children and teachers were filmed during a dyadic interaction task outside the classroom. Three groups of independent observers rated children's emotional security and their task behaviours, as well as teachers' supportive behaviours. Multilevel modelling revealed a positive link between teachers' support and emotional security. This link suppressed a negative relation between social inhibition and emotional security. In addition, emotional security was positively associated with children's task behaviours and mediated part of the positive link between these behaviours and teachers' support. Finally, security moderated the relation between support and persistence, such that the effect of teachers' support on persistent behaviours was amplified for relatively insecure children. These results highlight the importance of considering emotional security when examining the interactions between kindergarten children and their teachers. (Contains 2 figures, 3 tables and 5 notes.)