A new study finds students who attend schools with suspension policies for illicit drug use are more likely than students at schools without such policies to use marijuana in the following year.

The findings come from a survey of Australian students in 7th and 9th grades. Those who went to schools that suspended students for drug use were 1.6 times more likely than students at schools with more lenient policies to use marijuana in the next year. The increased marijuana use was seen even among students who had not been suspended, The Washington Post reports.

“That was surprising to us,” co-author Richard Catalano noted in a news release. “It means that suspensions are certainly not having a deterrent effect. It’s just the opposite.”

At schools where students caught with drugs were sent to their teacher to talk about the consequences of drug use, there was a 50 percent decrease in the odds students would use marijuana later on, the study found. Other strategies to dealing with drug use, including educational programs, referrals to a school counselor or nurse, expulsion, or calling the police, had no significant impact on marijuana use.

The study appears in the American Journal of Public Health.