The study aimed to identify the effectiveness of the School Leadership Training Program that is conducted by the Specialized Institute for Vocational Training of Teachers. The researcher examined the extent to which the program's objectives in developing the performance of school principals and their assistants in the Sultanate of Oman were met and provided recommendations for its development from the perspectives of school principals and their assistants, who have undergone the program. Following a quantitative descriptive approach, data were collected using an e-questionnaire; consisted of 32 statements in six sections that exemplify the objectives of the program under study. The study sample consisted of 120 principals and their assistants, and the data were statistically analysed using SPSS. The results of the study showed that the School Leadership Training Program is effective to a high degree. The results also indicated that there were no statistically significant differences at the level of significance (α ≤ 0.05) among the participants regarding the effectiveness of the school leadership program that could be attributed to the study's variables, namely: gender (male, female), job title (school principal, assistant principal), and academic qualification (bachelor's degree or less, master's degree or higher). However, the results of the study indicated that there are statistically significant differences at the level of significance (α ≤ 0.05) among the participants regarding the effectiveness of the School Leadership Training Program that could be attributed to the 'variable years of administrative experience', and it was in favour of the second group (years of administrative experience from (11-20 years). The study concluded with a set of recommendations; most importantly the need to continue to implement the training program for all leaders, including school principals and their assistants; the program effectively achieves its goals in developing their leadership skills.