Editor's note: Sarah Kovac is a motivational speaker and author of "In Capable Arms: Living a Life Embraced by Grace." The opinions expressed are solely the author's.
(CNN) -- How to discipline the next generation is a hotly debated topic. In 2012, a national survey showed more than half of women and three-quarters of men in the United States believe a child sometimes needs a "good hard spanking."
Science tells a different story. Researchers say physical punishment actually alters the brain -- not only in an "I'm traumatized" kind of way but also in an "I literally have less gray matter in my brain" kind of way.
"Exposing children to HCP (harsh corporal punishment) may have detrimental effects on trajectories of brain development," one 2009 study concluded.
Harsh corporal punishment in the study was defined as at least one spanking a month for more than three years, frequently done with objects such as a belt or paddle. Researchers found children who were regularly spanked had less gray matter in certain areas of the prefrontal cortex that have been linked to depression, addiction and other mental health disorders, the study authors say.
The researchers also found "significant correlations" between the amount of gray matter in these brain regions and the children's performance on an IQ test.
Several other studies support these findings. A 2010 study published in Pediatrics found that frequent -- more than twice in the previous month -- spanking when a child was 3 was linked to an increased risk for higher levels of child aggression when the child was 5.
Another, from the Journal of Aggression, Maltreatment and Trauma, found that corporal punishment doled out from the mother was independently related to a decrease in cognitive ability relative to other children. Corporal punishment had the largest effect on children 5 to 9.
Behind all this science-speak is the sobering fact that corporal punishment is damaging to children. That gray matter we've been spanking out of them? It's the key to the brain's ability to learn self-control.
"The more gray matter you have in the decision-making, thought-processing part of your brain (the prefrontal cortex), the better your ability to evaluate rewards and consequences," write the authors of a 2011 study that appeared in the Journal of Cognitive Neuroscience.
The sad irony is that the more you physically punish your kids for their lack of self-control, the less they have. They learn how to be controlled by external forces (parents, teachers, bosses), but when the boss isn't looking, then what?
Elizabeth Gershoff, an associate professor at the University of Texas at Austin, has been studying corporal punishment for 15 years, and is known as the leading researcher on spanking in the United States today. Over the years, Gershoff has done a systematic review of the hundreds of studies on the effects of corporal punishment.
"There's no study that I've ever done that's found a positive consequence of spanking," Gershoff said. "Most of us will stop what we're doing if somebody hits us, but that doesn't mean we've learned why somebody hit us, or what we should be doing instead, which is the real motive behind discipline."
Initially it was believed that spanking, at the very least, was associated with immediate compliance in children, and that parental warmth would buffer any harmful effects.
But the finding that spanking produced compliance "was overly influenced by one study," Gershoff said; it turns out spanking "doesn't make your kids better behaved. You think it does. ... It doesn't."
What is spanking associated with? Aggression. Delinquency. Mental health problems. And something called "hostile attribution bias," which causes children, essentially, to expect people to be mean to them.
This bias makes the world feel especially hostile. In turn, children are on edge and ready to be hostile back. Over time, across cultures and ethnicities, the findings are consistent: Spanking is doing real, measurable damage to the brains of our children.
And yet in 19 states, Gershoff notes, it is still legal for schools to paddle children.
For those thinking, "I was spanked, and I turned out fine," or, "I spank my kids and they're great!" consider that you don't know who you would be or how your children would behave in a world without spanking.
It could be that your children are thriving not because you spank, but in spite of it.