What it teaches
Opposite pairs, which are the easiest vocabulary of all to learn because each word carries the other one with it. A child who learns heavy alone has one word; a child who learns heavy and light has two and a relationship.
How it works
A word appears and the answers are words. Three levels change the round length and the number of answers offered.
The wrong answers are real words, often related ones, so the question cannot be answered by picking the only word that makes sense.
What to look for
Some pairs are not really opposites and a child will notice. The opposite of wet is dry, but what is the opposite of blue? Noticing that not everything has one is worth as much as the pairs themselves.