Although the No Child Left Behind (NCLB) Act refers to "low performing" schools as "in need of improvement," no one outside of the U.S. Department of Education uses that phrase. The term most commonly used is "failing." NCLB offers a single, explicit definition of a failing school: one that fails to make adequate yearly progress for two or more years in a row. (The recent safe harbor provision exempts schools that reduce the percentage of a failing subgroup by 10%.) This article discusses other ways to define a school's success or failure.