The present study examined how teachers' interpersonal behaviors (control, affiliation) and complementarity tendencies (i.e., return low control with high control and high affiliation with similar affiliation) were related to children's task behaviors (engagement, performance). Furthermore, we investigated whether the strength of these associations depended on children's externalizing and internalizing behaviors. Our sample included 48 teachers and 179 kindergartners (94 boys; mean age = 66.75 months) who were selected to represent a variation of externalizing and internalizing behaviors. Independent observers rated teachers' interpersonal behaviors and children's task behaviors. Teacher control was negatively related to both children's task engagement and performance, whereas teacher affiliation was not associated with children's task behaviors. Furthermore, associations between teachers' complementarity tendencies on control and children's task performance depended on the level of control that children displayed themselves. To conclude, teachers should be made aware that controlling behaviors could be detrimental for children's task behaviors. 1.1. Interpersonal theory and the complementarity principle According to the interpersonal theory (Leary, 1957), interaction processes can be described on two orthogonal dimensions: control and affiliation. Affiliation, which measures the affective quality of interactions, refers to the degree of proximity, warmth, and support in the interaction and varies from friendliness to hostility. Control, on the other hand, describes the degree of power and influence in the interaction and ranges from leadership/initiative to passiveness (Gurtman, 2001; Kiesler, 1996). As such, control refers to interpersonal qualities, such as initiative and leadership during interactions, instead of intrapersonal qualities, such as self-control and self-regulation (Eisenberg,