There is a great need to develop research-based models for supporting collaboration between educational institutions. Collaboration models are needed, for example, to assist the transition from lower educational level to higher education or from higher education to working life. In this research, collaboration was conducted through a joint course between upper secondary school and university, which addressed global challenges by using a project-based learning approach. There is a shortage of research exploring students’ perceptions of collaboration. Therefore, the main purpose of this qualitative case study is to explore the relevance of the joint course for upper secondary school students and university students. The research was guided by the following research question: What kind of relevance did the students experience in the joint project-based learning course? The data were gathered using questionnaires, interviews, and reflective study reports. The data were analyzed via theory-based content analysis, where research-oriented relevance model was used as the analysis framework. The analysis framework enabled categorizing experienced relevance on individual, vocational, and societal dimensions. Altogether, the analysis produced seven relevance categories for upper secondary students and nine for university students. According to the analysis, upper secondary school students felt that the course offered the most on an individual relevance dimension, whereas university students experienced the vocational relevance dimension a the most diverse. As the main conclusion, this research produced new insights on the experienced relevance of upper secondary level and higher education cooperation from the students’ point of view. The acquired knowledge can be useful for everyone developing new cross-institutional collaboration models.