App Recomendations

Khan academy. It's all on YouTube but there is an app that organizes it better. Great for math and history. They add videos every day. Really cool.

Slightly off-topic, but I've been meaning to post about this: If you're using PDD from an iOS device, the Wordpress app is great for creating posts and otherwise managing your account.

When in the App Store choose Education as the category.

I second the recommendation of Khan Academy. Unlike Wikipedia and some others, it's reputable.

I'd trust Wikipedia over a lot of other info apps...like Conservapaedia, for example.

I highly recommend Dragonbox.  It is the perhaps the only truly mathematically educational game that is also fun.  Most apps are either games with little educational value, or dressed-up drills.  Nothing wrong with drilling facts, but its hard to make it compelling.

Dragonbox might not be that much help in the near future, but I think it helps lay a foundation for learning algebra later on.

Khan Academy is OK, but is a little hit-or-miss - they do some topics better than others.  I'm not very impressed with their treatment of fractions and decimals, which is a key sticking point for 4th graders.