The University of California’s Dr. Baumrind, a psychologist known for her classic studies of authoritative, authoritarian and permissive styles of child-rearing, argues that an occasional spanking, when delivered in the context of good child-rearing, does not do any harm.

The study drew upon data from the Family Socialization and Developmental Competence Project, which followed families in the Berkeley, Calif., area over 12 years, from the time their children were preschoolers until they were adolescents.

Dr. Baumrind argues that, without compelling evidence that spanking is harmful, parents should be free to rear their children in accordance with their own values and traditions.

A majority of American adults still endorse spanking as a disciplinary tool, though that number has dropped over the last three decades. And a 1999 study found that 94 percent of 3- and 4-year-olds in the United States had been spanked at least once by a parent in the last year.

In deciding how to discipline their children, many parents say they rely on their pediatricians’ advice, the model provided by their own parents, their religious beliefs or their own experience of what works.

Michael Shannon, 47, of Clemmons, N.C., for example, says he and his wife decided years ago to spank their three children, now 15, 20 and 22, because they found that timeouts did not always work when the children were small.

My parents weren’t strict … but I knew where the line was straight away

”It seemed to get our child’s attention a lot quicker,” Mr. Shannon said.

He said he had been spanked with a paddle by his own father and did not believe it had negative effects.

”My parents weren’t strict,” Mr. Shannon said, ”But I knew where the line was right away.”