There are two elevators. One is blue. One is red. When you want to go up, you...

There are two elevators. One is blue. One is red. When you want to go up, you take the blue elevator. When you want to go down, you take the red elevator. It's that simple. It can't go wrong! The blue one only goes up. And the red one only goes down."
And so, at last, Wayside School got elevators. A blue one and a red one. They each worked perfectly one time - and never could be used again.