This study outlines a descriptive theory that seeks to grasp the complexity of the school as a state and societal institution as well as single schools as organizations. A significant characteristic of this complexity is the ambiguity of the missions and goals--the outer boundaries--of the school-institution. The more institutional ambiguity that characterizes these outer boundaries, the more extended is the available scope of action for single schools. To focus on the scope of action for single schools gives attention to the more and less extended latitude for conducting professionally-oriented school-development work. (Contains 5 figures and 9 notes.)