A bioluminescent growth arena. You are a number in a black ocean where everything obeys one radius law, so "smaller than me" is something you see before you read it. Then the water stills, four identical spheres rise, and only the times table tells them apart.
The pack suggests age 8 and up. The difficulty itself follows the player, not the age.

ARENA draws its questions from these parts of the curriculum. Which of them a player sees, and how hard the questions are, follows the player.