This study was designed to re-examine the effect of the school principal's instructional/educational behavior on student achievement in secondary schools. Previous studies found the school principal to play a pivotal role in school effectiveness measured by students' achievement. However, there is a considerable vagueness concerning the specific principals behaviors that influence students' achievements. Therefore, research questions were formulated in order to look for the effect of different domains of the principal instructional leadership behaviors on students' achievement. The research sample included 256 teachers from 32 secondary schools in Israel, who filled out the Instructional Leadership Behavior (ILB) for their school principals. Data about school features, such as, school size, average class size, teacher education and experience were collected. Theses variables were regressed on school students' achievements in the matriculation exams. The results indicate that 49% of the variance in students' achievement is explained by the following variables: Students' SES, class size, and only one leadership behavior, framing goals and communicating to staff.