In this paper, we report on the training practices of 12 mathematics mentor teachers who developed and implemented five short professional development courses after participating in a 5-month continuous professional development course "Competence-oriented teaching and learning of data analysis." The intention of this course was to deepen their professional knowledge of teaching statistics using digital tools, and to develop their competences and knowledge for developing and implementing their own professional development courses in statistics. Here, we explore how the professional program itself is reflected in the short courses they designed and implemented. Although the sample is very small, the cases allow for interesting insights into their training practices and challenges that seem to have a major impact on the quality of their professional development courses. On this basis we offer suggestions for how continuous professional development courses for mathematics mentor teachers might be designed to support their diverse needs in the professional development system.