What it teaches
Comparing quantities, and the signs that say so. Underneath, it is two sums and a judgement, which is more work than it looks and more like the maths a child will meet later.
It also keeps the idea of equality honest. Children who only ever see sums written left to right come to read "=" as "and the answer is". Comparing two expressions puts it back to what it means: the same amount on both sides.
How it works
Two expressions appear with a gap between them and three answers to pick from: bigger, smaller, or the same. The numbers follow whichever level is set.
A wrong answer keeps the question and shows the two sides being worked out, one at a time, before it shows which was bigger.
What to look for
Watch for a child answering by the size of the numbers rather than the size of the answers — picking the side with the 9 in it, for instance. It is a common and quite reasonable shortcut, and the game catches it quickly.