This case study presents the experiences of MSc Sport Psychology students delivering a psychologically informed behavior-change intervention within the context of a PhD research project to develop their applied practice skills. We aimed to provide an example of how higher education providers can create such an opportunity for master’s students to conduct individualized support sessions in a safe and structured environment, while preserving the autonomy needed for professional growth. The placement was situated within the HERizon project (conducted between 2021 and 2022), an online physical activity behavior-change intervention for adolescent girls. MSc students worked as “Activity Mentors” and provided weekly one-to-one support for participants via video calls. In this case study, we reflect on what we learned as both students and supervisors responsible for the delivery of HERizon, both immediately after completing the project and 3 years after the experience, and offer recommendations for future practice.