Ouch! A smack on the bottom does a lot of harm and no good.

One of the hardest parts of being a parent is figuring out how to teach your child right from wrong.

When your kid breaks a rule, do you talk things through? Stick him in a time-out chair? Take away his favorite toy?

And then there’s spanking, an age-old discipline technique that parenting experts tend to disagree on.

Is spanking an effective way to teach your kid a lesson? Canadian researchers dug through 20 years worth of published research to answer that question and they found that spanking fails to change a kid’s behavior and it can cause long-term damage.

The study, published this week in the Canadian Medical Association Journal, reveals that kids who are spanked are more likely to be depressed, aggressive, antisocial and anxious. They also tend to have lower IQs and as adults they’re more likely to have substance abuse problems and mental health issues. One study even showed that kids who were spanked are more likely to lie to avoid getting hit.

Of the 80 studies reviewed a few indicated that spanking has no or little negative effect on children, but not one study proved that physical punishment enhances developmental health.

Co-author Joan Durant, a professor at University of Manitoba, says the research clearly shows that spanking isn’t good for kids but the medical findings have long been overshadowed by a mindset that parents should have the right to decide how to discipline their children. Durant hopes the study will be a wake-up call to the parenting community and change the way we look at spanking.

“We’re really past the point of calling this a controversy. That’s a word that’s used and I don’t know why, because in the research there really is no controversy,” Durant told Reuters. “If we had this level of consistency in findings in any other area of health, we would be acting on it. We’d be pulling out all the stops to work on the issue.”

While spanking is less popular today than it was several decades ago, it’s still a widely used discipline technique. In a 2009 BabyCenter survey of 1,300 moms, 81 percent of moms said they were spanked as kids and 49 percent of those moms said they swat their own children. And last year, Tennessee pastor Michael Pearl made national news for the growing popularity of his pro-corporal punishment parenting book To Train Up A Child, which has sold over a half-million copies. Pearl told CNN that he represents 230 million parents who practice corporal chastisement on children in the name of God.

Durant hopes this study will put a stop to spanking and lead the medical world to direct parents to other forms of discipline. “What we’re hoping is that physicians will take that message and do more to counsel parents around this and to help them understand that physical punishment isn’t getting them where they want to go,” she told Reuters.

“If we had two or three studies that showed that if you took 500 mg of vitamin C a day you could reduce cancer risk, we would all be taking 500 mg of vitamin C a day,” Durant said. “Here, we have more than 80 studies, I would say more than 100, that show the same thing (about corporal punishment), and yet we keep calling it controversial.”