“Fathers, our daughters are waiting for us,” Mr. Wilson, 49, told the men. “They are desperately waiting for us in a culture that lures them into the murky waters of exploitation. They need to be rescued by you, their dad.”

The Wilsons organized what was considered the country’s first father-daughter purity ball 10 years ago, as their oldest girls entered adolescence. Randy Wilson is the national field director of church ministries for the Family Research Council, a conservative advocacy group, and Lisa Wilson is a stay-at-home mom.

“The culture says you’re free to sleep with as many people as you want to,” said Khrystian Wilson, 20, one of the Wilsons’ seven children, including five girls. “What does that get you but complete chaos?”

For the Wilsons and the growing number of people who have come to their balls, premarital sex is seen as inevitably destructive, especially to girls, who they say suffer more because they are more emotional than boys. Fathers, they say, play a crucial role in helping them stay pure.

“Something I need from dad is affirmation, being told I’m beautiful,” said Jordyn Wilson, 19, another daughter of Randy and Lisa. “If we don’t get it from home, we will go out to the culture and get it from them.”

Recent studies have suggested that close relationships between fathers and daughters can reduce the risk of early sexual activity among girls and teenage pregnancy. But studies have also shown that most teenagers who say they will remain abstinent, like those at the ball, end up having sex before marriage, and they are far less likely to use condoms than their peers.

No one knows for certain how many purity balls are held nationwide, because they are grass-roots efforts. The Abstinence Clearinghouse, an advocacy group, says it sells hundreds of purity ball kits annually to interested groups all over the country and abroad.