Apparently, a disproportionate number of them stop attending church. A curious statistic at Uncommon Descent:
75% of Christian youth leave the church after high school.
I assume that the churches get at least some of these young people back after they start having kids, but still. That’s an awfully high number, and it’s a reminder of how the 21st century world (at least in the United States) is simply not nearly as fertile ground for religion as one might suppose. Against the Bunyan-like Vanity Fair of media, electronics, and consumerism, and the temptations to secular gnosis from the Internet and the universities, evangelists and apologists have to work really, really hard to hold their flocks. In some ways, it makes it seem that the bells and whistles of the megachurches, with their coffee bars and contemporary music, reveal a weakness at the core of Christianity, not a demonstration of its ongoing cultural power.