Background: We leveraged a recent efficacy trial to investigate directionality between parent anxiety and child anxiety at posttreatment and 12-month follow-up, and the potential role of parent psychological control as a mediator. We also explored child age and sex as moderators.Method: Two-hundred and fifty-four children were randomized to individual cognitive behavioral therapy (CBT) or to one of two CBT arms with parent involvement.Parent anxiety was not a treatment target in any of the three arms.Results: Child anxiety at posttreatment was associated with parent anxiety and psychological control at 12-month follow-up, providing evidence of child-to-parent directionality. Parent anxiety at posttreatment was associated indirectly with child anxiety at 12-month follow-up through associations with parent psychological control, providing evidence of parent-to-child directionality. At posttreatment, parent psychological control contemporaneously mediated the relation between parent and child anxiety. Neither child age nor sex moderated any association.Conclusions: Findings highlight the directional effects between child anxiety, parent anxiety, and psychological control from posttreatment to 12-month follow-up, even when parent anxiety is not a treatment target. Research and clinical implications are discussed, with an emphasis on enhancing durability following treatment effects.