The younger boy is officially half-way through fourth grade math. We had him doing 20 minutes a day until about a month ago, and then we switched to 40 min per day (5 days per week). I decided to do this because it seemed like he'd finally get warmed up and make good progress and the program would quit on him. The funny thing is that his progress more than doubled. Not only was he better able to get into a groove, but he also retains it much better.
So we're fully expecting him to finish fourth grade math by the end of February and fifth grade math by the end of the year.
He has gotten upset that it's hard a couple times, saying he doesn't want to do it. He doesn't like it when he gets things wrong. I've had to sit down and say that, yes, it is hard. However, it's okay to get things wrong sometimes, and he really seems to have fun once he gets into it. He likes to figure things out, and you can tell he's proud of himself when he struggles through something and then finds the answer. I think this is helping him to work through some of his perfectionistic tendencies.
I'm very glad we talked the school into this arrangement. It's going far better than we expected.