As the number of charter schools continues to grow, one facet of their autonomy--the ability to set and enforce independent disciplinary standards--has raised difficult questions about whether those schools are pushing out students who pose behavior or academic challenges and how their policies affect regular public schools. Research on the issue is sparse, and data on expulsions and disciplinary incidents at charter schools paint a nuanced picture nationwide. But in a few urban districts where high discipline rates at charter schools have drawn scrutiny, school officials have recently taken steps aimed at ensuring that students in both charter and other public schools are treated fairly. The promise and appeal of charter schools hinges partly on the idea that their freedom from many of the state and district policies that govern regular public schools allows for more effective schools. Some experts on charters, though, say increased accountability on disciplinary issues in the sector is overdue.