The purpose of this study was to investigate the effectiveness of school principal’s leadership in school improvement program in Wolaita Zone government secondary schools. Descriptive survey research design was employed to describe the phenomena to the study. In Nine woreda , ten secondary schools were selected through simple random sampling. 10 students’ representatives under sample woreda and 30 principals were selected through availability sampling technique. Furthermore, 120 teachers participated in the study by using simple random sampling technique. Questionnaire was prepared for teachers and principals. Focus group discussion and document analysis were also used to validate the data gathered through questionnaires. Frequency, percentage, standard divisions, means and person’s correlations were used to determine the relationship between variables. The result of the study indicated that educational leaders ineffectively providing textbooks and other teaching/learning materials mission, and goals of the school, creating a Conducive environment to facilitate supervisory activities in the school by organizing all necessary resources, curriculum monitoring and evaluation and low participation of stake holders improving SIP implementation for effectiveness of principal’s leadership. Besides this, principals used several approaches in supervising the implementation of instructional practices. Some approaches like use of students to monitor teacher lesson attendance and visiting class to observe a teacher were rarely used. Most principals involved their subordinates in decision making. Schools faced challenges that include inadequate trained teachers and learning/ teaching materials, inadequate science laboratories and lack of time to check on the teachers’ and students’ work by principals. Study recommends that the school provide more learning materials and facilities like science laboratories and libraries. The woreda education office have better to employ more teachers to the schools with understaffing in order to relieve the current teacher of the work load and ensure timely syllabus coverage as this will significantly impact to effectiveness of principals. Principals have better to delegate mores duties to their stake holders in order to save time to assess both the students’ and teachers’ commitment to their work.