When parents lift their hands

But times have changed, and so has Straus' perception of spanking.

"If I knew then what I know now, I would not have spanked them at all," he says. "My research has convinced me that there should be no hitting -- never, under any circumstances."

Straus, co-director of the Family Research Laboratory at the University of New Hampshire, has long advocated doing away with spanking. And many psychologists and pediatricians also now say that parents should never strike a child. Assemblywoman Sally Lieber (D-Mountain View) has even promised to introduce a bill in the California Legislature that would make it illegal to hit those younger than 4.

Frequent and impulsive spanking is clearly detrimental, researchers agree. Other kinds of physical punishment, including hitting children with objects, are harmful as well. "Corporal punishment has really serious side effects," says Alan Kazdin, a professor of psychology at Yale University and president-elect of the American Psychological Assn. "Children who are hit become more aggressive."

Yet the mildest forms of spanking have not been proved harmful. "A family that hits once in a while? The research is equivocal about that," Kazdin says.

What the research does show is that spanking is generally no more effective than nonphysical disciplinary techniques in instilling acceptable behavior, that its effects vary from culture to culture and that a greater frequency of spanking increases the risk of negative consequences.

Although some researchers say it can play an occasional role in supporting more lenient forms of discipline, Kazdin argues that spanking should be avoided even if it is harmless.

"It suppresses [misbehavior] momentarily. But you haven't really changed its probability of occurring," Kazdin says. "Physical punishment is not needed to change behavior. It's just not needed."

Reasons not to spank

Spanking can escalate toward physical abuse, potentially injuring the child, and can contribute to later emotional and behavioral problems, according to the American Academy of Pediatrics. It's also less effective than alternative disciplinary tactics, and it's a hard habit to break, the organization says. Studies have shown that people who were spanked as kids tend to spank as parents, perpetuating the cycle.