Based on Fiedler's Contingency Model of Leadership Effectiveness and Leader-Match program, this study's hypothesis is that experienced school principals increase their effectiveness by changing key organizational variables to suit their personal leadership styles. Following V. D. McNamara's application of Fiedler's contingency model in a study of elementary school principals, Feidler has suggested that organizational leaders can maximize their effectiveness by manipulating leader-member relations (the extent to which leaders feel liked and accepted by the group), task structure (the degree to which leaders can define and control tasks), and position power (the leader's formally delegated power as distinguished from the ability to inspire loyalty). To test four hypotheses examining the congruence between leadership style and school organizational structure in light of the differences between "open" and "traditional" schools, Faulkner's Description of School questionnaire was distributed to 400 randomly selected schools in 25 Ontario school districts. A one-way analysis of variance computation for the 156 schools finally used in the study supports three of the four hypotheses and confirms the explanatory power of Fiedler's contingency model. Results also indicate, however, that further study is needed of outside social forces as important contingencies for leader effectiveness. (JBM)