The study aims at identifying the first phase of the Post Basic School Administration and Supervision Competencies Application in the following districts (Muscat, South Batinah, the Interior) and at revealing the differences in the response of the participants according to the variables related to gender, the educational qualification, experience, and district regarding the reality of the School Administration and Supervision Competencies Application. To achieve the aims of the study, a descriptive approach has been opted for. A survey of 60 sections concerning the 8 chapters of the study has been given and applied on 618 teachers, males and females. After the statistical analysis of the results using the statistical bundle SPSS, the study revealed the following findings: The Post Basic School Administration and Supervision Competencies Application scored high percentages at all levels of the study except at two that scored average: (Headmaster competencies in strategic planning, headmaster competencies in implementing school culture). The findings have also revealed statistical differences related to gender in favor of the females in the headmaster competencies in strategic planning, and in the headmaster competencies in engaging parents in the strategic decision making. The findings have also revealed statistical differences particular to the South Batinah region in their estimation of the headmaster's competencies in the strategic planning implementation, and to the Interior and the South Batinah regions in their estimation of the headmaster's competencies in implementing the school culture. The findings have also revealed no statistical differences related to experience and educational qualification. The study suggests carrying out another study on the professional development for basic school headmasters in Oman, and another study on the development of educational supervision in Oman, taking advantage of other countries.