These police-driven policies have not made schools safer. But they do make children more likely to drop out and become entangled with the justice system. And they disproportionately affect minority and disabled children, who are more likely to be singled out for the harshest forms of discipline.

The Obama administration has made combating this problem a priority. It has increased civil rights investigations and required some school districts to rework their disciplinary policies. Last year the Justice Department’s Civil Rights Division and the Education Department’s Office for Civil Rights jointly issued detailed guidelines showing school districts how to reduce arrests and reform practices in which black students are disciplined more harshly than white students engaging in similar behavior as well as to curb the use of punishments — like mandatory expulsion, suspension or ticketing — that have a disproportionate and unjustified effect on students of one race.

Such police-driven discipline is even used against the very young. The Justice Department filed court papers last month in support of a civil rights lawsuit brought by the parents of two disabled children — one 8 years old, the other 9 — who attended public school in Kenton County, Ky. Both children have severe disabilities that make it difficult for them to follow instructions. In both cases, a deputy sheriff responded to misbehavior by handcuffing the children. Their arms were so tiny that the cuffs were applied at the biceps.

The 8-year-old had been found to have attention deficit hyperactivity disorder and post-traumatic stress disorder. According to court documents, a video of the incident shows the child writhing and crying in pain as the officer berates him, saying, “You can do what we ask you to or you can suffer the consequences.” As a result of the incident, the government maintains, the child continues to suffer emotional distress. The actions of the officer clearly violated the Americans With Disabilities Act.

Children with disabilities are particularly vulnerable to this kind of disciplinary abuse. Federal data show, for example, that they represent 12 percent of the student population but 25 percent of children who get one or more out-of-school suspensions and 23 percent who are subject to arrest for school-related misbehavior.