The principals' leadership is the most important factor in determining the development of schools. In order to improve education quality, the principals' leadership competences should be improved. The aim of this study is to test the effect of self-evaluation as the technique of the self-development of the principals' transformational leadership and its effect on teachers' work motivation, teamwork effectiveness and school improvement. The study was conducted in Malang, Indonesia. It used quasi-experimental research design with non-equivalent comparative group. The subjects of the study were 40 principals and 240 teachers for each experimental groups, and 40 principals and 240 teachers for the controlled group. They were chosen using cluster quota random sampling. The instrument used to collect the data was questionnaires including behaviour observation scale, numerical scale and summated rating, while the data analysis techniques were statistic descriptive, univariate and multivariate analyses of variance. Based on the data analysis, it could be concluded that the self-evaluation technique was effectively proven in improving transformational leadership, teachers' work motivation, teamwork effectiveness and school improvement. The model of self-evaluation with feedback has a stronger effect compared to self-evaluation without feedback.