It is true that the retention rate (the rate at which children raised in the faith stick with it as adults) is somewhat higher among fundamentalist Christians than it is among mainstream Protestant groups. However, it's still not good: the odds are probably better than even that kids raised in either group will not be practicing in those same groups by midlife.

In particular, over 50% of all fundamentalist kids who attend secular college have left the fold entirely after four years. (The bulk of that group leaves in the first two.) This is, in fact, why fundamentalist parents hate sending their kids to secular schools -- how are you gonna keep 'em down on the farm after they've seen State U?

But college isn't the only place attrition is high. A lot of people who leave deeply conservative religions make the break at other life transition points. Leaving home (even if not for college), marriage, widowhood or divorce, the death of a parent, and retirement all seem to be major turning points where our religious beliefs either sustain us, or prove to be disappointingly inadequate to the job.

The midlife crisis of the late 30s may be the biggest one of all. At this point in life, we have the confidence to question authority, and the seriousness of mind to demand good answers. It's a time of earnest seeking and self-creation. While some people are drawn to authoritarian religion as part of this phase, it's often a temporary experiment that's over in a few years (the long-term retention rate for these folks isn't great) and their families seldom join them. At the same time, those who've grown up in these churches can be drawn away from them during this period of seeking. They're likely to be gone for good -- and they usually take their spouses and half-grown children with them when they go.

Taken altogether, I'd be surprised if one in three kids born into fundamentalist homes are still practicing the same faith at 45. If that guess is anywhere near accurate, these families would have to raise six babies to ensure that there were still two adults in the pews half a century hence. While they may have one or two more kids on average, that's still nowhere near the rate needed to achieve this.

The current best research (I think it's Pew's stuff) reveals the real trend we need to discuss: The number of Americans who consider themselves secular, and have no church affiliation, has been steadily rising for the past couple generations and shows no signs of slowing. While the mainstream churches have taken the bulk of that hit, this fact still puts the lie to fundamentalist crowing that they're going to somehow outbreed us.

Let's not help them validate this idea. There's plenty of reason to doubt its essential truth.