-- The pending child abuse case against Minnesota Viking Adrian Peterson has brought spanking, a common form of child discipline used by parents, back into public scrutiny.
"By the the time they reach adolescence, 85 percent of the nation's children will have been, at one point or another, spanked," Dr. Alan Kazdin, a psychologist at Yale University told ABC News. The figure comes from a 2003 study in which Kazdin investigated the use of spanking in disciplining children.
And between 70 percent and 90 percent of Americans admit to using some form of physical force when disciplining their kids, according to Southern Methodist University psychology professor George Holden.
"Physical punishment is extremely common for young children," Holden told ABC News. "It's very common in the United States."
Kazdin's 2003 study defines spanking as "hitting a child with an open hand on the buttocks or extremities with the intent to discipline without leaving a bruise or causing physical harm."
But while spanking is prevalent, it is ineffective, Kazdin said.
"You don't need spanking to change behavior," Kazdin said. "It is not effective at all. It increases aggression in children, has emotional consequences."
The line between spanking and more serious physical abuse is often muddled by theoretical and practical definitions, Kazdin said.
His study defines physical abuse as "corporal punishment that is harsh and excessive, involves the use of objects ... is directed to other parts of the body than the extremities, and causes or has the potential to cause physical harm."
Kazdin notes that parents can sometimes use objects in what would routinely be considered a spanking.
"He used the same kind of discipline with his child that he experienced as a child growing up in east Texas," the statement read. "Adrian never intended to harm his son and deeply regrets the unintentional injury."
Peterson was booked and charged with reckless or negligent injury to a child, a felony, in Montgomery County, Texas, on Saturday morning. He was released after posting $15,000 bond.
Texas law defines child abuse as "an act or omission that endangers or impairs a child's physical, mental or emotional health and development," according to Texas' Family Code.
But the state makes an exception for "reasonable discipline" by the child's parent or guardian.
"Corporal punishment is not in itself abusive under the law," according to a statement from the office of Texas Attorney General Greg Abbott.
Physical discipline, like a spanking, would only become abusive if "observable and material impairment occurs as a result," according to the statement.
Parents in every state can legally hit their child as long as the force is "reasonable."
Coporal punishment is also allowed in schools in 19 states, including Texas, according to the Center for Effective Discipline.