This research aims to determine the professional standards required of in order to define the school administrative position in Turkey. It utilizes mixed methods research approach. Focus group interviews with 30 participants in three sessions with 10 participants from each group were conducted in three non-governmental organization schools based in Istanbul, Ankara, and Corum provinces in Turkey. Through the 7point Likert-type questionnaire -Professional Standards Scale for School Leaders (PSSSL) - was developed by the researcher and 328 members in NGOs founded by school heads and educational leaders in Turkey were sampled. The factor analysis of the scale with 0.994 internal consistency coefficient showed that 77.2 professional standards of school leadership was explained. According to research results, proficiency areas of school leaders determined were: (1) knowledge base, (2) effective communication, (3) institution management, (4) change leadership, (5) technology leadership, (6) educational leadership, (7) school-environment relations and (8) life and society. The results of the current research will be useful for defining school leadership duty as a profession, obtaining professionally required personal employee rights, reorganizing school leader training programs, and relevant NGOs to be able to establish internal auditing mechanisms.