The McKinsey Group has released a new follow-up report to their 2007 publication "How the world's best performing school systems come out on top." The new report, "How the worlds' most improved school systems keep getting better," looks at the approaches that 20 international school systems that are in different stages of the path to excellence (or lack thereof) use for improvement (systems are divided in moving from "poor to fair", "fair to good", "good to great", "great to excellent"). The obvious lesson is that depending upon where you are on this path, different interventions are needed. I thought you might find this report interesting since you work with schools that are in different places on the journey to excellence. This isn't a short document, but if you have a little time, you might find it interesting.
http://www.mckinsey.com/clientservice/Social_Sector/our_practices/Education/Knowledge_Highlights/How%20School%20Systems%20Get%20Better.aspx