Comparing your kids, the kids of educated professionals, to the Duggars really isn't fair. I've worked in enough schools with kids from families that aren't as educated or whose parents just don't care, and those kids would never have made it through that book in first grade.
Jessa is marginally educated. Ben has a degree, but how much of his love of learning is he passing on to his kids? He's not their primary educator.
I'm in the middle camp of Spurge understanding some but not all of what he "read."