Examined the extent to which improvement in parent training varied as a function of children’s ages (early vs middle childhood). 73 families with distressed children (age 2.5-12.5 yrs) were observed interacting in the home at pre- and postintervention. The children’s levels of observed aversive behavior were compared with those of 27 nondistressed families. 63% of the distressed children aged <=6 yrs showed clinically significant change, compared to 54.3% of the children aged >=6 yrs. A repeated measures ANOVA on observed aversive behavior revealed a statistically reliable pre- and posttreatment improvement (phase), and a general effect for the age of the child. The phase-by-age of the child interaction was nonsignificant. Examination of families who failed to complete training revealed a high representation of older children (aged 6.5-12.5 yrs) compared with younger children (2.5-6.5 yrs).