More and more research shows that far from curbing a child’s behavior problems, spanking actually increases them.

The latest entry into this canon found children who have been spanked by their parents by age 5 show an increase in behavior problems at age 6 and age 8, compared to children who have never been spanked, according to new findings in the journal Psychological Science.

The study, which uses a statistical technique to approximate random assignment, indicates that this increase in kids’ bad behavior cannot be attributed to other characteristics of the child, the parents, or the home environment — rather, it seems to be the specific result of spanking.

“Our findings suggest that spanking is not an effective technique and actually makes children’s behavior worse not better,” says psychological scientist Elizabeth T. Gershoff, of the University of Texas at Austin, the study’s lead author.

Historically, trying to determine whether parents’ discipline via smacking a child on the bottom actually causes her to develop behavior problems has been difficult, because researchers cannot ethically conduct experiments that randomly assign parents to spank or not.

“Parents spank for many reasons, such as their educational or cultural background or how difficult their children’s behavior is. These same reasons, which we call selection factors, can also predict children’s behavior problems, making it difficult to determine whether spanking is in fact the cause of behavior problems,” Gershoff explained. “We realized that the statistical method of propensity score matching could help us get as close to an experiment as possible.”

Gershoff and co-authors Kierra M. P. Sattler and Arya Ansari examined data from 12,112 children who participated in the US’s nationally representative Early Childhood Longitudinal Study. When the children were 5 years old, their parents reported how many times they had spanked their child in the past week (if any). The researchers classified any child whose parent provided a number other than zero as having been spanked.

The researchers then matched children who had been spanked with those who hadn’t according to 38 child- and family-related characteristics, including: the child’s age, gender, overall health, and behavior problems at age 5; the parent’s education, age, and marital status; the family socioeconomic status and household size; and factors related to parenting quality and conflict in the home.

Pairing the children in this way yielded two groups of children whose main difference was whether their parents had spanked them, effectively accounting for other factors that could plausibly influence the behavior of both parent and child. This approach allowed the researchers to approximate the random assignment of participants to groups, a hallmark of credible experimentation.

To gauge children’s behavior problems over time, Gershoff, Sattler, and Ansari examined teachers’ ratings when the children were 5, 6, and 8 years old. The kids’ teachers reported the frequency with which the children argued, fought, got angry, acted impulsively, and disturbed ongoing activities.

The results were clear: Children who had been spanked at age 5 showed greater increases in behavior issues by age 6 and also by age 8 when compared with children who had never been spanked.

Gershoff and colleagues conducted a similar analysis with only children who had been spanked by their parents, comparing children who had been spanked in the week before the study (which suggests frequent spanking) and those who had not. Children spanked in the past week at age 5 also experienced greater increases in problem behavior at age 6 and 8 compared with children not spanked as frequently.

“The fact that knowing whether a child had ever been spanked was enough to predict their levels of behavior problems years later was a bit surprising,” says Gershoff. “It suggests that spanking at any frequency is potentially harmful to children.”

So spanking as a form of discipline is out — not just because it’s not particularly nice to hit anyone, including kids, but also because punishments for kids don’t really accomplish what parents want: changed behavior. Instead, try this proven, effective technique at changing bad behavior long-term.

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