Leo copied the answers without reading the story. The next day, when Mrs. Gutierrez asked him, "Why did Alejandro go to the library in Bogotá?" Leo had no idea. He had the answers, but he had missed the entire adventure.

Leo wrote about how Alejandro learned that the greatest treasure was not gold, but the ability to understand and speak with people from different cultures. Leo got an A. And he never confused Buenos Aires with Lima again.

In a bright, bustling classroom in Madrid, a teacher named Mrs. Gutierrez handed out a thin, green booklet to each of her students. The title on the cover read: La Gran Aventura de Alejandro , a popular Spanish reading workbook for intermediate learners. The story inside followed Alejandro, a young explorer from Seville, who traveled through Spanish-speaking countries solving riddles.

She held up a piece of paper with the words "La Gran Aventura de Alejandro – Clave de Respuestas (Answer Key)" at the top. But this was no ordinary answer key. It was a she had created herself.

"Señora," said a student named Leo, "how will we know if we correctly conjugated the preterite vs. the imperfect tense in Alejandro's conversation with the Mayan historian?"

Mrs. Gutierrez smiled. "That is part of the adventure. But," she added, pulling out a printed sheet, "I have something that will help you learn, not just check boxes."

The students loved the story, but they soon faced a problem. After finishing a chapter about Alejandro escaping a maze in Mexico City, they had to check their answers. The problem? Mrs. Gutierrez had the only answer key, and she had locked it in her desk.