Recent research shows that principals can heavily influence schools' organizational effectiveness. This report describes the instructional leadership roles of elementary and high school principals participating in the Wayne State University Staff Development for School Improvement Program (SDSI) conducted from 1981 through 1984. The SDSI school improvement model is included, along with important characteristics of staff development programs in 15 participating schools. The program is based on teachers' ability to identify their own priorities and collaborate to meet their needs--with the principal's support. Each school received modest funding to be used for staff development activities and a facilitator to guide participants through the six-step process. A recent evaluation found that at least 82 percent of the teachers in each school observed improvements in knowledge, skills, communication, and participative decision-making. Most commonly mentioned strengths were increased involvement in planning school activities and improved staff morale. Program success was greatest when activities were conducted during released time, when there was minimal staff turnover, and when support from the district and the principal was present. Included are tables, seven references, and the author's