My Take
Stack the States is a winner on several levels; the game play is truly fun, and students will enjoy balancing the states on top of each other (not easy to land Texas on New Hampshire!), it reinforces basics such as state capitols and nicknames, and it gives a great visual for comparative state size. Additional mini-games are built in to aid in learning the placement of states. Terrific app for students in grades 3-6.
The knowledge reinforced is only recall, but we do expect students to learn the states and be able to place them on a map, and this highly visual game helps.
How I Use It
I've used this app with the Apple TV to play the game with an entire class--they love shouting out the answers and taking turns balancing the states. It is also used individually for students who enjoy the game play and the test of their knowledge.