What Disruption Really Is
Clayton Christensen's notion of the power disruptive innovations have is put in perspective by this excellent post from Matt Yglesias in Slate. Yglesias points out that some so-called innovations are really about taking an extant idea and doing them much, much better; e.g., Apple's iPod supplanting existing-but-inferior MP3 players. Seen through this lens, the iPod was less a disruptive innovation in and of itself and more of a refinement or perfection of someone else's good idea.
The point for independent and international schools looking to innovate is that one starting point is to take an existing idea (think online or blended education, year-round school, pay-for-performance) and refine it to smooth out the rough edges and mitigate the barriers to widespread adoption. (Almost) everything is derivative.