An app that makes kids do educational app in order to unlock game app?

Has anyone come across an app that could be set up by a parent so that the kids would have to first do an educational app in order to unlock a game app? Ideally, especially for somewhat older kids, the app would require a result, e.g. 3 words spelled correctly, from a selected installed educational app before allowing access to selected installed game apps for a specified amount of time. But if that was too difficult the app could simply require the educational app be open for a selected amount of time before allowing the game app to be played.

I often tell my kids they need to do something “educational” on the computer or iPhone before they get to randomly surf at pbskids, or, ok I’ll admit it, play angry birds. But it would be easier if it was required by the app or computer program, so it didn’t sound like mom nagging them again. I think pbskids can be educational too, but not in a specific, curriculum-based way.

When my kids sit down at their computer it would be so cool if, for example, all the icons except Little Musician were dimmed out and they had to complete the 5 minute daily curriculum before getting access to the other icons.
Many of the educational apps, such 24 x 7 Digital’s Teach Me series, are designed so that the kids complete activities to earn rewards. This would be a similar concept except that an activity in one app would be rewarded by unlocking another app.