Abstract Background: Several systematic reviews have demonstrated the efficacy of cognitive behavioral therapy (CBT) treating anxiety disorders in children and adolescents (hereafter referred to as youths). Treatment of anxiety disorders conducted by student therapists (ST) has been found to be an effective alternative, to treatment conducted by psychologists. Objective: The primary aim of the study is to investigate the effects of ST treating youths, using a group-based CBT program. Second, the study aims to compare these results with outcomes achieved by professional-therapists (PT). Method: The study investigate in an open trial design, the treatment outcome from a manualized CBT program (Cool Kids) in a group of youths (n = 54) treated by ST. Results are benchmarked against the outcomes of a group of youths (n = 56) treated by PT using the same program, derived from a separate randomized controlled trial. Results: There was a significant reduction of both self-reported and clinician rated measures of youth anxiety over time in the ST group, with small to large effect sizes. No significant differences of improvements in self-report measures were found between the ST and the PT groups. There was no significant difference in remission rates for participants’ primary anxiety disorder between the ST (50.0%) and the PT (66.1%) at post-treatment or at three-month follow-up (ST: 74.1%, PT: 76.8%). There was a significant difference regarding number of youths free of all anxiety disorder between the ST (14 [25.9%]) and PT (27 [48.2%]) group at post-treatment. This difference was not significant at three-month follow-up (ST: 25 [46.3%], PT: 33 [58.9%]). Conclusion: The findings support previous findings, suggesting that student-therapists, receiving training and supervision, can successfully treat youths with anxiety disorders using a manualized CBT program. The outcomes following CBT treatment conducted by ST are comparable to outcomes achieved by PT.