Although many higher educational institute (HEI) psychoeducational courses teaching positive psychology interventions report benefits to mental well-being upon completion, they have not typically addressed whether such beneficial effects are sustained long-term beyond the period of the courses. Here, we report a pre-registered follow-up of 228 undergraduate students, from a variety of disciplines, who took a positive psychology course 1 or 2 years previously. Overall, group analysis revealed that students who had taken the course did not continue to show the originally reported benefits at follow-up. Students who had taken the course scored higher on mental well-being than other students tested using a university-wide survey, but they were also higher at baseline 1-2 years earlier indicating a sampling bias. An exploratory analysis, however, revealed that 115 students (51% of the group) who had continued to practice the recommended activities taught during the course maintained their increased mental well-being over the period of follow-up. We therefore suggest that continued engagement is a key factor in sustaining the long-term benefits of positive psychology courses. Implementation of such courses should therefore include provision and mechanisms for maintaining future student engagement.