Researcher George Holden set off to study how often parents yelled at their children, but after listening to 36 hours of real-time audiotapes he heard something else; the cracks of spanking and the screams that followed.

Most of the behavioral incidents were "petty" in nature, according Holden, a professor of psychology at Southern Methodist University in Texas, but the punishment was "virtually all highly inappropriate." In one incident recorded on tape, a mother spanked her 3-year-old 11 times for fighting with his sister and the boy is reduced to tears and coughing. One child was punished for not cleaning his room. Another was slapped for being overzealous during a bedtime story by pointing and turning the page. "They were pretty shocking," said Holden, who has written five books on child development.

"They highlight that so much of corporal punishment are misguided notions of parenting that are bad for the child," he said. "It's sad that a parent inadvertently ruins the quality of their relationship by jumping on the child for being a normal kid." The study, "Real Life Mother-Child Interaction in the Home," was conducted over six nights, when parents and children were most tired. Holden found 36 mothers and one father at Dallas day care centers who agreed to leave a tape running between the time they got home and put the kids to bed. The parents were evenly divided from all economic backgrounds. Most were white and a third were African-Americans.

So as not to skew the study, they were told that it was about parents' interaction with their children. "The vast majority -- 90 percent of parents -- admit yelling at their kids, but we didn't have a good data what is it like," he said. But the tapes showed more than yelling.

"We have not totally coded all the tapes yet, so we actually expect to find a lot more examples of this inadvertent window into parents' use of corporal punishment," Holden said. "It presents a unique view that no one ever had before about what goes on in these families." Holden presented his study this month in Dallas at the Global Summit on Ending Corporal Punishment and Promoting Positive Discipline and it was reported in Time magazine. Spanking is universally condemned among most child development and parenting experts, although some fundamentalist Christian groups disagree, citing the Biblical passage, "Spare the rod and spoil the child." Holden said spanking is likely pervasive because it is "such an entrenched practice," and it is difficult to convince parents otherwise.

"They are not a separate class of people who would be classified as child abusers," he said. "A lot of moms on the tapes would have defended their use of corporal punishment, at least in the abstract. Parents are under the impression that it's a good childrearing technique." Holden agrees that an "occasional spank" might not have a long-term negative effect on a child, "unless it was so hard it resulted in child abuse or injury." "The problem is when parents rely on physical punishment, they are more likely to escalate when the kids misbehave if they do not stop," he said. "They come back and they hit harder and are indeed more at risk to abuse them." Research shows that parents who rely on spanking for discipline encourage negative behaviors, including aggression. Children can also show signs of depression and anti-social behavior as they grow older. "There are also some links to bullying," Holden said.

But Robert Larzelere, a psychologist in the department of human development and family science at Oklahoma State University, argues that "conditional spanking" -- two swats with an open hand on the bottom -- is not detrimental to a child.

Conditional Spanking Can Be Effective, Says Critic One of the most vocal opponents of spanking bans, Larzelere said non-abusive spanking is more effective on 2- to 6-year-olds than a dozen other tactics, including reasoning, verbal threats, privilege removal, ignoring, bribes, restraint and diversionary tactics. "When you look at all the studies, conditional spanking led to less disobedience and less aggression," he said.

The only other method as effective as conditional spanking is putting a child in a "4 by 5-foot empty closet" for a minute, he said. "A boring, safe room." He said spanking should be used to "back-up" time-out when a child is defiant. Milder methods should always be considered first. "Of course, if parents use spanking too severely or as the primary method, the outcomes are more fighting and more problems," said Larzelere. "Parents need to learn all kinds of tactics that are most effective so they don't have to get to the point where they use spanking. But it does back up all other tactics." Larzelere agrees with Holden that parents always try a positive method first, but "sometimes kids need negative consequences."

Murray Straus, professor of sociology and co-director of the Family Research Library at University of New Hampshire, agrees that spanking works. But the point, he said, is that so do non-violent methods, without the so-called side effects. And spanking has a big "short-term failure rate," he said. Children, particularly toddlers, will repeat behaviors regardless of punishment and must do so to learn. "With a 2-year-old nothing works," said Straus. "It takes hundreds of corrections over and over, and you have to be consistent and persistent. ... But it all works in the long run. "The best established studies all show that without exception, [spanking] increases aggressiveness," he said. "They are more likely to hit other kids and also more likely to hit their parents." When parents spank, they don't do it typically the first time, they do it when other things don't work and that sets a bad example.

"A normal kid -- not a bully or mean kid -- when someone is squirting water at him and they don't stop after repeatedly asking, will follow the same script," said Straus. Surprisingly, said Straus, parents -- even college educated ones -- don't get that message because child development books devote so little space to the topic of spanking. "I have surveyed books from the 1980s, 1990s and 2000s, and despite all the studies, they get a half a page in one of these giant books," he said. "Not a single one says, 'Don't spank.' "The belief in American society is hard to shake. But parents believe in their heart of hearts that spanking works when others things don't."

He said he was impressed with Holden's research, which might help experts understand why spanking continues, "especially in this era." As for Holden, he said his inadvertent study "shows what really goes on in homes."

"Every single mainstream parenting program teaches parents how to raise kids without physical punishment," he said. "There are plenty of places to turn to get help in the challenging task of childrearing. We have three and I survived."