Both a branch of the NGO Intize and several projects of the math department of the Europa-Universität Flensburg (EUF) focus on providing mathematical education to specially gifted or interested school students. The concepts of both project partners are structurally similar. The central idea of the projects is that young university students as mentors lead weekly meeting groups of school students. In these groups the mentors as role models not only teach math but act as a guide and counsellor for the school students regarding a professional or academic career in STEM. We designed the mobility project so that the mentors from Sweden could share knowledge and experiences with mentors from Germany at the EUF. This strengthened both groups of mentors as well as the organisations. Moreover, the intercultural exchange aimed at professionalizing the mentors by collaborating with academics from a foreign country. These experiences not only fostered the mentors regarding their personal development but also their teaching. It is both encouraging and beneficial to meet peers with similar experiences. One goal of the exchange is that the mentors will be inspired, encouraged to keep giving their time to this cause and that all mentors will be more skilled and efficient in meeting their group of mentees after the project. The exchange was not limited to the mentor level. By establishing a long-term connection between the project leaders not limited to this particular project, permanent structures on organisational level were created. Besides the mentors, project leaders, and the organisations as a whole also the participating school students benefitted. One part of the project was the mentors giving math online courses in international mentor teams for international audiences of German and Swedish school students. So the project aimed for exchange on three levels: The whole organisations, the mentors and the school students.