America’s Teenage Girls Are Not Okay

American teenagers—especially girls and kids who identify as lesbian, gay, bisexual, or questioning—are “engulfed” in historic rates of anxiety and sadness. And everybody seems to think they know why.

Some psychologists point to social media, whereas others blame school shootings; others chalk it up to changes in parenting. Climate-change activists say it’s climate change. Atlantic writers like me blather on about the decline of physical-world interactions. These explanations aren’t equally valid, and some of them might be purely wrong. But the sheer number of theories reflects the complexity of mental-health challenges and suggests that, perhaps, nobody knows for sure what’s going on.

The numbers are...