Abstract Medical Advice for Sick-reported Students (MASS) is an intervention that aims to reduce medical absenteeism and prevent dropout among students. The current study reports on a process evaluation of the implementation of MASS at a vocational school in the Netherlands. The evaluation included the implementation process, fidelity, context, and participant satisfaction. The study had a qualitative case study design. Data was gathered through semi-structured interviews with relevant stakeholders, including a child and youth healthcare physician, MASS coordinators, career advisors, mentors, and students with concerning sickness absence. MASS was largely implemented as intended, but some deviations from the original intervention were found. For example, not all mentors identified concerning sickness absence through recommended criteria. A fit between the intervention and the values of the involved organizations was found. Facilitating contextual factors were identified, such as a perceived need for reducing school absence recognized within the care network, as well as hampering contextual factors, for example the limited visibility of students’ absence during the COVID-19 pandemic. Participants were generally satisfied with MASS and its implementation. Overall, MASS was implemented well according to interviewees, but several improvement points for both the implementation and execution of MASS were identified. These include full implementation across the setting, providing and repeating necessary trainings, minimizing administrative burden, and securing financial and human resources for sustainment of the intervention. These points could help to guide future implementation efforts, as they may help to overcome common barriers to implementation.