From Remy Melina, LiveScience Staff Writer

Few parents of teens who drink or smoke pot are aware of it, suggests a new study that also finds that most parents are concerned about substance use by teenagers and believe that more than half of 10th-graders drink alcohol (just not their own 10th-grader).

Only 10 percent of parents think their own teens drank alcohol within the last year, and 5 percent believe their teens smoked marijuana in the last year, according to the latest poll by the University of Michigan’s C.S. Mott Children’s Hospital.

These low numbers severely clash with the university’s 2010 Monitoring the Future survey, in which 52 percent of surveyed 10th-graders reported drinking alcohol in the last year and 28 percent reported using marijuana within the last year. Those numbers were based on an annual survey of about 420 public and private high schools and middle schools that are selected to provide an accurate representation of U.S. students at each grade level.

“There’s a clear mismatch between what parents are reporting in terms of their children’s possible use of substances and what teenagers report themselves,” said study researcher Bernard Biermann of the department of psychiatry at the University of Michigan. He is also a medical director of the university’s Child/Adolescent Inpatient Unit.

The C.S. Mott Children’s Hospital National Poll on Children’s Health was administered in May to a group of 667 parents with a child between the ages of 13 and 17.

While most parents seem to assume their own kids aren’t trying alcohol or drugs, they certainly don’t think their child’s peers are as innocent. In the poll, researchers found that many parents of teens are very likely to believe that within the last year at least 60 percent of 10th-graders drank alcohol and 40 percent of 10th-graders used marijuana.

That parents are more likely to expect drug and alcohol use by other teenagers than by their own indicates a need for awareness about teenage substance use, the researchers said. They suggest parents broach the subject with their teens in a nonthreatening way and speak to them about the importance of resisting peer pressure.

“Awareness is a means of opening the door to communication. If parents acknowledge the possibility — and in fact, the likelihood — that their child may have experimented with or used alcohol or marijuana, they can begin to talk to them more about it, provide some guidance, and allow their kids to ask questions,” Biermann said in a statement.

The researchers also suggest that parents carefully monitor their kids and look for signs of substance use. They warn parents not to overreact over a single instance of substance use, and to instead use the experience as an opportunity to talk to their teen in a nonjudgmental way.