That the use of physical punishment to discipline kids is a heated topic goes without saying. Over the last 20 years, many countries have passed laws to protect children from physical punishment in school and elsewhere, but the research shows that many parents still use it to discipline their kids.

A new Canadian study reviewed two decades of research on spanking and found not only that, "...[N]o study has found physical punishment to have a long-term positive effect, and most studies have found negative effects."

Luckily, studies have also shown that when parents are given help to stop physically punishing their kids, their kids’ difficult behaviors also decrease.

Depression, aggression, anxiety, feelings of hopelessness, drug and alcohol use, and “general psychological maladjustment.” were among the problems seen in children who were spanked. As children who have been spanked become adults, they are more likely to become aggressive themselves since they have seen adults solving problems aggressively. According to the authors, "...virtually without exception, these studies found that physical punishment was associated with higher levels of aggression against parents, siblings, peers and spouses."

There are a variety of mechanisms to explain these psychological changes. It is certain that physical punishment disrupts the important emotional connection between parent and child. In this way, spanking is not one-time, isolated event. It changes the child's relationship with the parent.

Imaging studies have also shown some important changes in the brains of children who were punished physically. Decreases in the gray matter of the brain have been seen in regions connected to IQ. And the dopamine system that plays a role in drug addiction risk is altered in kids who were the subjects of physical punishment.

Luckily, studies have also shown that when parents are given help to stop physically punishing their kids, their kids’ difficult behaviors also decrease. This suggests that not only is there a cause-and-effect relationship between parents’ use of physical punishment and negative behaviors in kids, but that once parents stop using this form of discipline, kids’ behaviors actually improve.

The American Academy of Pediatrics does not recommend the use of physical punishment on kids, since they say it is “the least effective way to discipline.” More effective and healthier methods of discipline include timeouts, logical consequences, or behavior penalties. See the AAP website for recommendations on the best ways discourage bad behaviors in your kids and encourage the good ones.

The authors, affiliated with the University of Manitoba and the Children's Hospital of Eastern Ontario, hope their study will encourage pediatricians to counsel parents against spanking. "Effective discipline rests on clear and age-appropriate expectations, effectively communicated within a trusting relationship and a safe environment." The study is published in the February 6, 2012 issue of the Canadian Medical Association Journal.