It was a study by the Southern Baptist Council on Family Life. What methodology they used I don’t know.
I don't know either. Seems to me it would be a very difficult study to do rigorously and scientifically.
I do recall that when one of my siblings was a troubled teenager, my mother said she kept telling herself, "The Bible says 'Raise up a child in the way he should go, and when he is old he will not depart,' but it doesn't say he won't take some detours between the time he's young and the time he's old."
What really amazed me was a segment I heard on NPR yesterday afternoon saying that most people did not understand Mike Huckabee's Biblical references, such as to the stories of David and Goliath, the loaves and fishes, and the widow's mite.
It does seem that fewer and fewer children go to Sunday school, though...this year I asked my students if they had ever heard of Noah and the Ark, and maybe 1/3 to 1/2 seemed to recognize the story...