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It’s not P.C. to admit you spank your child. But nearly 40 moms have gone a step further, recording themselves hitting and slapping their kids as part of a new study on how parents and children interact.

They didn’t know they were going to be in a study about spanking per se. Researchers have to be careful when presenting their proposed area of study to potential participants — too much information can lead people to alter their normal behavior, which would skew results. So when George Holden, a professor of psychology at Southern Methodist University who has published five books on parenting and child development, went to day-care centers in Dallas to recruit parents, he divulged only that he wanted to collect data about naturally occurring parent-child interaction.

In fact, Holden didn’t even know he’d be studying spanking. He originally set out to study yelling, via voluntary audio recordings of parents conducting life at home — the pedestrian stuff of parenting like meal prep, bath time and lights out.

Not all parents who volunteered were accepted. Researchers eliminated those who reported during a screening interview that they never yelled at home. “There weren’t many,” notes Holden, who presented the research this month in Dallas at the Global Summit on Ending Corporal Punishment and Promoting Positive Discipline.

Here’s the twist: in the course of analyzing the data collected from 37 families — 36 mothers and one father, all of whom recorded up to 36 hours of audio in six days of study — researchers heard the sharp cracks and dull thuds of spanking, followed in some cases by minutes of crying. They’d inadvertently captured evidence of corporal punishment, as well as the tense moments before and the resolution after, leading researchers to believe they’d amassed the first-ever cache of real-time spanking data.

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The recordings feature a mother spanking her 3-year-old son 11 times for fighting with his sister, prompting a fit of crying and coughing. Another mom hits her 5-year-old when he won’t clean up his room. One mom slaps her child when he doesn’t cooperate with the bedtime routine.

I don’t know about you, but if I’m going to be recording my interactions with my kids, I’d be on my best behavior. (Note to researchers: don’t include me in any parenting studies.)

Yet it’s likely that the mothers in the study didn’t consider spanking to be problematic behavior. In the 1990s, Holden conducted research that showed 70% of college-educated women spank their children; other studies have found that up to 90% of all parents use corporal punishment.

Children who are spanked occasionally are not thought to be significantly impacted later on, but those who are spanked regularly are more likely to have behavior problems that may escalate into antisocial behavior. They may also be at greater risk for anxiety disorders or depression and ultimately may be more likely to engage in domestic violence and child abuse as adults.

Yet although it makes sense that getting hit is not good for kids, there have not been any longitudinal studies dividing children into “spanked” and “non-spanked” groups and tracking any emotional and behavioral consequences over time. The existing research relies instead on self-reported data, based on memory.

Parents in the domestic trenches are probably not all that interested in what the research shows anyway. Despite a battery of disciplinary techniques, including the infamous “time out,” redirection and the increasing emphasis on positive discipline (try substituting “hold the cup carefully” for “don’t spill your juice”), spanking and slapping are still pretty popular.

Moms and dads who spank do so because they believe it’s effective, and research actually shows that it is — in the short-term. A child reaching for a tempting object will stop if he gets swatted. “It does work in the immediate moment, but beyond that, in most cases, it’s very ineffective,” says Holden. “The most common long-term consequence is that children learn to use aggression.”

Case in point: one mother in the study hit her toddler after the toddler either hit or kicked the mother, admonishing, “This is to help you remember not to hit your mother.”

“The irony is just amazing,” says Holden.

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Holden’s recordings provide rich context for what causes a parent to spank. The data are particularly unsettling because many of the infractions that led a mom to hit involve petty misbehavior, like turning the page in a book before it was time. While listening to his mother read The Tortoise and the Hare, for example, one boy began touching the pages, garnering a slap.

“At 2:03:31, the mother says, ‘No, Justin,’ and continues reading,” according to a transcription describing the incident. “Then at 2:03:34 she smacks him, and says, ‘No, Justin. If you want me to read, quit messing with the pages. Cause you’re moving it while I’m reading.'”

The parents who recorded themselves represented a socioeconomic mix: a third each were low-income, middle-income and upper-middle-class or higher. Most were white; about a third were African-American.

Researchers broke down the data, detailing each spanking or slapping incident, what led up to it, what type of punishment was used and how much, how a child reacted immediately and then several minutes later.

“The idea is this data will provide a unique glimpse into what really goes on in families that hasn’t been available through traditional methods of self-report,” says Holden.

There’s some evidence these days that parents are spanking less, says Holden, although the majority still consider hitting a useful form of discipline. Most parents are at least what Holden calls “very occasional spankers.” Until recently I placed myself in this category too. But even “very occasional” was too much for me. Swatting my child — no matter how disrespectful she’s been — is never worth the guilt I feel afterward, so I have pledged to my kids that those days are over.

Together, my quick-tempered 6-year-old and I have agreed to place our hands on our bellies — a technique she learned in kindergarten — to calm ourselves. It really works: it breaks through the fog of angry words and it feels much more genuine than slapping a hand as a form of discipline. Hitting teaches that it’s O.K. to turn violent when you’re mad, which is not a lesson I’m eager to impart.