Bob - I think the biggest factor in a child continuing with the faith (thus showing that they had a true, saving faith from the beginning) is having a family that walks the walk - not just in public but in private as well. How do you deal with crisis in the home? How do you deal with disagreements? How do you deal with attacks? Or even how do you deal with daily life? I think it equips them to be able to deal with the real world better than just tossing them out there and hoping for the best.
I homeschooled the girls through 8th grade but they did attend public school for 9th -12th and both went to secular colleges and continue a strong walk with the Lord - strong enough to be discipling other girls.

But I think it was the foundation of being home and watching us live our faith daily and just how to submit to God's control in everything. THAT makes a huge difference.
That and amazing grace.