Although middle-level school principals are essential to current school reform, their professional development is one of its most neglected aspects. Research, literature, and support in this area are scarce and poorly coordinated. This paper reports on research done to create a conceptual framework within which characteristics for effective professional development could be identified. Some characteristics are that development should be directed toward local school needs; should involve participants in program planning, implementation, and evaluation; should put the principal into the role of learner; and should involve mentoring of principals in their school settings. Data collection was done using surveys and semistructured interviews with 175 middle-level principals. Central questions included: What do they now want and need to learn? Where do they want to learn it? and How will they learn it best? Results show that professional development for middle-level principals should be based on their expressed needs; should involve them in the planning, implementing, and evaluation of such activities; should take place in a supportive cohort structure; should be long-term and backed by time, money, and resources from the district; and should be conducted by competent presenters who utilize adult-learning processes in addressing practical issues. (Contains 47 references.) (RT)