I like your original take on the theme! The pixel art looks goofy, I particularly enjoyed the teacher characters: they look hilarious.
The card game itself is good, too. Once I figured out how the average grades affect time spent on task, it was pretty easy to beat the game. The tutorial could have been improved, because during my first playthrough I didn't understand what is going on, but still there is enough information to figure out game mechanics on your own right now.
Maybe it would be fun if rules changed in the second half of the day somehow or if there were some random events.
Great job! Good luck to your team of Uncles in your future projects!