The aim of this study was to determine the efficacy of the four telephone contact sessions that are prescribed as an integral component of the Group Triple P parenting program, and to compare the efficacy of Group Triple P to a waitlist control group. Parents of children aged 2 to 8 years were randomly assigned to one of three conditions: the usual Group Triple P program, consisting of four group sessions and four telephone calls (n = 16); a modified Group Triple P condition, consisting of just the four group sessions (n = 17); or a waitlist control condition (n = 16). Pre- and post-intervention assessments were conducted using the Eyberg Child Behavior Inventory (ECBI), the Depression Anxiety Stress Scales (DASS) and the Parenting Scale (PS). Statistically and clinically significant main effects were found for attending either the full Triple P or the modified Triple P program on both the DASS and the ECBI, but not on the participant's perception of their parenting style (PS). We conclude that (a) the four telephone sessions are not an essential component for the initial effectiveness of the Group Triple P program (though further research needs to explore whether they impact on maintenance of gains), and (b) that Group Triple P is effective in bringing about change, as measured using these self-report instruments.