The school systems making the largest gains are united by some common threads: Government and school leaders have set aside differences and harnessed their power behind reforms, superintendents have brought an intense, persuasive leadership style to the process, and efforts have concentrated on raising the test scores of the lowest-performing students.
But Philadelphia also illustrates how hard it can be to sustain improvements. The superintendent credited with much of the gain, Paul Vallas, is leaving the city this month as budget projections show a large deficit threatening his reform program.