This study focused on examining the treatment effect associated with two 12-session interventions (child-centered play therapy and nature-based child-centered play therapy) among early elementary schoolchildren (N = 8) who had an attention-deficit/ hyperactivity disorder diagnosis. Children were randomly assigned to one of the treatment groups or the waitlist group. We found that the child-centered play therapy intervention ranged from debatable (n = 1) to effective (n = 2) and the nature-based child-centered play therapy intervention ranged from debatable (n = 1) to very effective (n = 1), with one participant also scoring in the effective range for improving on-task behavior. In comparison, the waitlist group participants had a large fluctuation in scores, with the analysis revealing that noninvolvement in treatment was ineffective for improving on-task behavior. © 2018 Association for Play Therapy.