The program -- Talking Parents, Healthy Teens -- was developed by a team led by Dr. Mark A. Schuster of Children's Hospital Boston, while he was at Rand Corp.

Researchers randomized 569 parents, employed at 13 large public and private work sites in Southern California, to participate in the program or to serve in a control group.

Some parents attended eight weekly lunch-hour sessions and, through role-playing and other interactive exercises, they learned techniques for starting and sustaining conversations on sex-related topics -- using creative opening lines and identifying their children's conversational roadblocks. Through "active listening," parents were taught to listen to their children without interrupting or starting to lecture.

Between weekly meetings, parents practiced at home, playing games designed by the program with their children or discussing a variety of sex-related topics.

"The great thing was that the parents really learned," says Schuster, who is also co-author of the book "Everything You Never Wanted Your Kids to Know About Sex (But Were Afraid They'd Ask.)"

The findings are published in the British Medical Journal.