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.