Piaget put the same amount of water into two different glasses: a tall narrow glass and a wide glass, then asked kids to compare two glasses. Kids younger than six or seven usually say that the tall narrow glass now holds more water, because the level is higher. And when they are ready, they figure out the conservation of volume for themselves just by playing with cups of water. Piaget argued that children's understanding of morality is like their understanding of those water glasses: we can't say that it is innate or kids learn it directly from adults. Rather, it is self-constructed as kids play with other kids. Taking turns in a game is like pouring water back and forth between glasses. Once kids have reached the age of five or six, then playing games and working things out together will help them learn about fairness far more effectively than any teaching from adults.