Stack the States is a fun way to test grade-schoolers’ knowledge of state capitals, shapes and abbreviations. Each time you answer a question correctly, a state drops into your platform. Your challenge then becomes to rotate the states and fit them together like puzzle pieces with the ones that are about to drop from above. Once the states are stacked and you cross the finish line, you earn a state for your permanent collection. When you have mastered the app and collected all 50 states, download Stack the Countries to upgrade your knowledge to include national flags, landmarks and much more.