While this blog post from the Center on Great Teachers and Leaders on utilizing a distributed leadership framework to assess and support school leadership, is a bit dated, it still holds true. Here's an excerpt:

"State education agency (SEA) and local education agency (LEA) leaders can seize the opportunity to advance research-based principal effectiveness systems that are worth the time and effort required for implementation. These systems must provide useful, timely, and relevant data and feedback, and they must recognize the changing role of the school principal. Contrary to the popular culture perception of the principal as a metaphorical superhero who, by herself or himself, can enter a struggling school and 'save the day,' recent literature shows an increasing need for and acceptance of distributed instructional leadership: a strategy that uses the work of many formal and informal leaders within a school to enhance student learning."