The effectiveness of school principals was studied with the goals of: identifying skill dimensions related to principals' performance; identifying a set of independent psychological constructs from a factor analysis of those dimensions; and using the variables of school size, district size, school grade level, and geographic region of Washington State to test a universal trait and behavior approach to describing effective leadership. A review of literature on effective school leadership identified 39 skill dimensions related to effective performance of school prinipals. Supervisor ratings were obtained for 583 principals (a 38.7% response rate) across the 39 skill dimensions and 10 State performance standards. Data analysis demonstrated that 37 of the skill dimensions had significant positive correlations with the 10 measures of job performance. Fifteen dimensions had correlations above 0.6 with overall performance. Factor analysis suggested that the following constructs accounted for 61.4% of the variance: (1) instructional leadership; (2) interpersonal skills; (3) organizational commitment; and (4) personal drive and motivation. Chi square, correlational, and t-tests confirmed the universality of the 37 skill dimensions and four major constructs across the four moderator variables. More effective principals had higher ratings on the same 37 dimensions regardless of the situational factors. The rating sheets used are included. Three tables give information about the study and the factor analysis. Recommendations to enhance school leadership are made based on the findings. (SLD)