Christine cut off her daughter’s Internet access for months, mandating that she write schoolwork by hand. Over time, the girl earned back computer privileges. Christine also moved her to a parochial school. Then her daughter went on Facebook.

“We didn’t know much about Facebook,” said Christine, “but we set up serious monitoring.” One program limited computer time; another blocked certain sites. Christine even had her daughter’s Facebook password, so she could read the girl’s private messages.

That was how Christine discovered 82 exchanges between her daughter, a freshman, and a popular senior boy at the school. Her daughter offered him oral sex if he promised not to tell friends. The boy wrote back, “Would it be O.K. if I tell friends but not the ones at school?”

Christine’s daughter now sees a therapist. Christine herself uses a keystroke logger, software that records everything her two daughters write and see on their home computer. “It’s uncomfortable,” Christine said. “But my older daughter has demonstrated less than zero common sense. The level of trust between us is much lower than I’d like it to be. But I also think she was relieved that we caught her.

“My younger daughter calls me a stalker. She says we mistrust her because of what her sister did. That’s true. But my eyes are open, and I won’t go back.”

Studies show that children tend to side with Christine’s younger daughter. Last April in an omnibus review of studies addressing youth, privacy and reputation, a report by the Berkman Center for Internet and Society at Harvard noted that parents who checked their children’s online communications were seen as “controlling, invasive and ‘clueless.’ ” Young people, one study noted, had a notion of an online public viewership “that excludes the family.”

Conversely, studies show that more parents are heading in Christine’s direction. A recent study of teenagers and phones by the Pew Research Center Internet and American Life Project said that parents regard their children’s phones as a “parenting tool.” About two-thirds said they checked the content of their children’s phones (whether teenagers pre-emptively delete texts is a different matter). Two-thirds of the parents said they took away phones as punishment. Almost half said they used phones to check on their child’s whereabouts.