CZERKA-FORTUNA, Eliza. Learning Systems. Development of Professional Competences of School Heads and Teachers. Przegląd Badań Edukacyjnych (Educational Studies Review). Online. 29 November 2018. Vol. 2, no. 27, pp. 167-181. [Accessed 27 April 2024]. DOI 10.12775/PBE.2018.023.