Juan, Sarah and Laura are building sand castles. But which one's tallest? Juan's is only two shovels high, while Sarah's is three. Laura's moat is one big spoon deep, while Juan's is two little spoons deep. Too bad their shovels and spoons aren't the same size. But "an inch is always an inch," says Larry the Lifeguard, using a tape measure to determine the winners.

Children learn that it is helpful to use standard units of measure to make accurate comparisons.