Many researchers have examined the impact of Headmasters' managerial or leadership styles on school improvement. They have found either positive, negative or no impact of Headmasters' roles on school improvement. Very few researchers have inquired to what extent a school changes if principals' roles and teachers' professional development work together with same spirit. Therefore, this researcher has tried to find whether the relationship between principals' roles and school improvement become strong, weak or neutral with the presence of third variable teachers' professional development. This...