Quality educational leadership preparation has positive influences on practices of graduates. In the Finnish decentralized education system, little is yet known about the sources of principals' practices. This research explores the sources of principals' self-assessed leadership practices in Central Finland and identifies areas for more emphasis. Respondents were selected by purposive sampling. This multiple case study employed eight semi-structured individual interviews as means of data collection. Inductive content analysis was performed. From the findings, besides personal experiences, knowledge from course, and field work, leadership and networking are also major sources of principals' practices. Training positively enhances the practices of principals as they engage in more collaboration and trust. Notwithstanding, professional development is essential for principals to stay relevant to the contemporary world of today and to be confident to face future challenges. Methods of course delivery, management of human and financial resources, as well as creating and sustaining local and international collaborations with other training institutions should be prioritized to improve on training.