The study aims to disclose the relationship between the school effectiveness and the principals Leadership Style in the 20d Cycle schools of basic education in the Sultanate of Oman and the procedures proposed to promote the performance of the schools directors to realize effectiveness in the schools of basic education. To achieve the objectives of the study, the researcher analyzed the theoretical background and the literature review relevant to the objectives of the study. In addition, a questionnaire of 97 statements was composed representing two aspects: The first aspect was the leadership style represented by two dimensions: the moral dimension and the work pattern dimension. The second aspect was the school effectiveness, represented by four dimensions: adaptability, integration, achievement of objectives and potentiality. The study sample consisted of (413) male and female teachers from the 2nd cycle schools of basic education (5-10) from two educational governorates: Muscat governorate and Dhofar governorate, and two educational regions: Al Batinah north and Al Batinah south. The statistical processing was carried out using mean averages, standard deviations, relative significance (rank), (T –test) for two independent samples, (ANOVA) and Schaffee's test for post-hoc comparisons. Some of the most significant findings of the field study are the following: 1-The study sample's total assessment of the level of school effectiveness in the 2nd cycle schools of basic education in the Sultanate of Oman is high. 2-The principals of the 2nd cycle schools of basic education gave more emphasis to productivity and the methods of achieving work (following setting up the pattern of work) than the morals between themselves and the teachers. 3- The most common leadership style in the 2nd cycle schools of basic education are the style A, democratic and D, the lenient. 4- With regard to the impacts of the variants, the study reached the following findings: There are statistically significant differences at the = 0,05 level between the average disparities of the study sample's assessment on the (adaptability and achievement of the declared objectives) dimensions attributed to the variant of kind in favour of the females while it is in favour of the males in the dimension of integration in the processes of discipline). There are no statistically significant differences that can be attributed to kind in the potentiality dimension. • There are statistically significant differences at the 0,05 level between the averages of the study sample's assessments in all dimensions of the study attributed to the variant of academic qualification. Among the intermediate diploma and MA holders it was in favour of the diploma while among the BA and MA holders it was in favour of the BA. . There are statistically significant differences at the 0,05 level between the averages of the study sample's assessments in all dimensions of the study attributed to the variant of experience in favor of the medium experience. There are statistically significant differences at the 0,05 level between the averages of the study sample's assessments in all the dimensions of the study attributed to the educational region between Dhofar governorate and Al Batinah ņorth region in all four dimensions in favour of Al Batinah region. There are statistically significant differences at the 0,05 level in the school effectiveness with its four dimensions (adaptability, achievement of goals, integration of processes and potentiality) attributed to the leadership Style. Style A, the democratic, scored the highest level in all dimensions of school effectiveness. In the light of the analysis of the literature review and the findings of the field study, the study has reached a number of proposed procedures of which the most important are: intensifying the school principals' training courses on how to employ the various leadership style to develop their communication skills to promote school effectiveness. The ministry should provide the schools' principals with websites and the addresses of websites concerned about the development and renewal of school effectiveness. The ministry should also organize workshops for the schools' principals to improve their efficiencies in the use of modern technologies in management and other workshops to train them on the methods of improving the motivation, loyalty and satisfaction of the teachers, besides the development of a practical plan to implement the concept of co operation at work to score the highest possible effectiveness