Purpose: The purpose of this paper is to explore the strategies and an effective model for creating and implementing a sustainability internship program at a university campus. Design/methodology/approach: This study assessed Western Michigan University's sustainability program's interns' gain of environmental knowledge on sustainability topics via pre- and post-test assessments. A sample of 50 interns between fall 2016 and spring 2019 comprising six cohorts participated in this study. Data were analyzed using statistical package for social sciences to calculate descriptive statistics and sign tests. Findings: The sign tests of the accumulative internship pre- and post-test assessment scores significantly increased for all 14 sustainability knowledge dimensions. Research limitations/implications: The pre- and post-test assessments of the internship program are unable to track and predict the long-term behavior changes of the interns after the completion of the program. Therefore, a future longitudinal study is needed. Practical implications: This sustainability internship program's content and experiential learning model has been proven to be effective in increasing interns' knowledge of sustainability issues and creating sustainability stewards. Institutions and universities should consider creating their own sustainability internship program based on Western Michigan University's program using pre- and post-test assessments as a method of evaluation. Social implications: The internship programs' main strength is that it offers students from all academic backgrounds an opportunity to dig deep into sustainability issues, build new social networks, gain knowledge, develop leadership skills, become sustainability stewards and immediately apply what they have learned on campus and in their local community. On-campus internships are unique learning opportunities worthy of study and refinement. Originality/value: This research paper is unique because it analyzes the combined pre- and post-test scores of six cohorts of interns' across multiple knowledge dimensions of sustainability. This study empirically shows that the combined interns' sustainability knowledge across all dimensions significantly increased from the pre- to post-test over the semester-long program.