Because numbers vary widely by school district, the prevalence of suspensions appears to correlate more with policy than it does student behavior. Suspensions have come to serve as a proxy for school climate—and on campus, climate, as anyone who went to school knows, can be warm and embracing or severe and righteous, depending on the district, school, and even classroom. "No-excuses" charter networks, such as Uncommon, Achievement First and KIPP, have managed to get low-income students to graduate and enroll in college at higher rates than the national average. Yet as Sarah Carr reported in The Atlantic last year, the strict discipline policies of these networks, whose methods have filtered into many urban-district schools, alienates many students. And some experts have concluded that these approaches are unnecessary.

In the stereotypical urban school, fights break out in hallways and hair gets set on fire in the stairwells (I remember both happening at my urban public school in the early ‘90s). Leaders at these schools, in turn, may feel they have no choice but to institute tough-love rules.

The Princeton researcher Joanne Golann observed an unnamed no-excuses urban charter school in the Northeast over the course of a year and a half between 2011 and 2013 and is slated to share her results in a paper that will be published next month in Sociology of Education. She cites one middle-school principal who witnessed the before-and-after of a strict discipline policy, explaining, "we had students who tried to burn down the school, students who brought weapons." When the principal installed typical no-excuses rules—mandates that students walk in straight lines between rooms or sit in silence if a teacher raises two fingers, for example—the atmosphere of the school apparently calmed and test scores went up. The principal concluded that "what works in urban education are rigid structures and hierarchical relations," Golann said.

But Golann points out that no one actually knows for sure if zero-tolerance practices are critical to the schools’ success. "The schools believe that they are," she said. "But actually the research evidence is much more mixed." Any positive impacts of no-excuses schools may lie more in supplementary features such as longer school days and intensive tutoring.

Getting suspended for minor offenses may even be counterproductive if a school's goal is preparing kids for college and their careers: The practice enforces obedience more than the kind of independent thinking valued by four-year colleges, according to Golann. KIPP has even publicly expressed concern that it might be able to get low-income kids to college but not keep them there at rates comparable to those of higher-income students, in part because they need to develop the self-advocacy skills familiar to children who have been taught to negotiate for themselves throughout their lives.