U.S. Education Secretary John King on Tuesday urged Tennessee and 21 other states to stop allowing corporal punishment in schools, a practice he called “harmful, ineffective, and often disproportionately applied to students of color and students with disabilities.”

The nation’s education chief instead advocated the use of disciplinary measures that create a positive school climate and promote nonviolent techniques for conflict resolution.

King outlined his concerns in a letter to the governors and education chiefs of states that allow disciplinary techniques such as paddling or spanking.

“…  The very acts of corporal punishment that are permissible when applied to children in schools under some state laws would be prohibited as criminal assault or battery when applied to adults in the community in those very same states,” King wrote in his letter.

Corporal punishment is defined as intentionally inflicting pain to punish a child or in an attempt to change behavior. The U.S. Supreme Court ruled in 1977 that the practice does not violate constitutional rights. Tennessee is one of 15 states, most of which are in the South, that have policies allowing corporal punishment in public schools. Seven more indirectly allow it by not having a specific ban in place.

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Tennessee’s two largest school districts — Shelby County Schools and Metropolitan Nashville Public Schools — have banned corporal punishment, but it’s still allowed in several districts across the state.

Data collected by the U.S. Department of Education shows a racial gap in how corporal punishment is dispensed. Black boys are 1.8 times as likely as white boys, and black girls are 2.9 times as likely as white girls, to receive the disciplinary measure. And in nearly all of the states where the practice is permitted, students with disabilities were subjected to corporal punishment at higher rates than students without disabilities. Boys are also disproportionately impacted.

“These data and disparities shock the conscience,” King wrote.

King cited myriad research showing that physical punishment actually exacerbates poor behavior, rather than correcting it. Students that receive corporal punishment are more likely to be depressed or show antisocial behavior as adults.

One of the alternatives King proposed is restorative justice, which aims to address the root causes of disagreements and misbehavior through conversation rather than punishment. The practice is already gaining steam in schools in both Memphis and Nashville.

“The most frequently cited rationale (for corporal punishment) tends to be tradition and concern about how schools can ensure safe and orderly environments,” he told reporters in a briefing on Monday. “… (But) there are smarter ways to achieve safe and supportive environments.”

The letter comes as Tennessee grapples with school discipline data showing that school suspensions are concentrated at some of the state’s poorest, most segregated schools and disproportionately impact students of color.

Tennessee Department of Education spokeswoman Sara Gast said the state is redoubling efforts to promote “healthy and fair” discipline practices.

“Our state law specifically notes that each local board of education is responsible for adopting any rules they deem necessary on this topic,” she said. “While corporal punishment is legal, our state training and resources promote the use of restorative practices to foster positive discipline in schools.”

Disparities in discipline have been a rallying cry for the Obama administration, which has launched several initiatives aimed at decreasing racial disparities and increasing the use of alternatives to suspension, expulsion and corporal punishment.

It’s unclear how the administration of President-elect Donald Trump will approach the matter, but the head of the nation’s largest teachers union urged continued advocacy against corporal punishment, even as Obama’s administration ends.

“It does not matter who the secretary of education is. … This is a moral matter,” said Randi Weingarten, president of the American Federation of Teachers. “I don’t care if you are a Republican or a Democrat, a conservative or a progressive. …There is no earthly justification for paddling, caning or otherwise physically harming students in schools.”