One day the authorities of Nicaragua decided to do something for the deaf children. They decided to teach them sign language so that they could communicate with the rest of the world and not turn into languageless zombies.
So they started a school for deaf children and began teaching them sign language. Problem was, the children didn't learn very fast or well.
What happened was that instead of learning the sign language the teachers tried to teach them, they naturally created their own sign language among themselves. All of a sudden, the teachers noticed the children joking and arguing in the school yard, and they didn't understand a word of what the children were saying to each other. Ironically, the teachers were now trying to learn the sign language from their pupils.