We have been using the “Visits to…” series nearly since we began homeschooling five years ago. We have 3 books left to complete and my son is entering high school. I would like to revisit the continents which haven’t been touched in a while. What do you guys use to help retain what they’ve learned from year to year? I can only imagine how much of Africa has been forgotten by now. Do you employ a simple computer drill program or what? Thanks.