Child temperament has long been viewed as a potential susceptibility factor in the link between parenting and child disruptive behavior (CDB). Specifically, the idea is that children with higher negative emotionality, surgency, and lower effortful control are more affected by their received parenting, but experimental evidence is scarce. Also, others have argued that child temperament might not be a susceptibility factor but a factor that can change through parents' participation in a parenting intervention. To test both hypotheses, we analyzed pretest, posttest, and 4-month follow-up data from 386 mostly Dutch parents, mainly mothers (92%; M[subscript age] = 38.1, SD = 4.8) with children (M[subscript age] = 6.31, SD= 1.33; 54.2% boys). The children had above-average disruptive behavior (i.e., [greater than or equal to]75th percentile Eyberg Child Behavior Inventory questionnaire; Eyberg & Pincus, 1999). The families participated in a randomized controlled trial of the Incredible Years (IY) parenting program. Hierarchical regression analyses showed that child temperament did not moderate IY intervention effects on CDB. Furthermore, parallel process analyses showed that the IY intervention led to direct, simultaneous decreases in both negative emotionality and CDB. These findings counter the widely held belief that temperament traits are static, unchangeable modulators of the links between parenting and CDB. Instead, child temperament (negative emotionality) can at least partly be influenced by parents' participation in a parenting program.