Haiku are a major form of verse in Japan. These poems have a 5-7-5 syllable requirement. They're never more than that, with each number being one line of the haiku. You can make this a cultural lesson as well as an English lesson to keep the students' interest. For instance, come to class dressed in a kimono and read some traditional haiku. Or you could bring some more modern examples, such as reading from the book of Zombie Haiku. The offbeat nature will make the lesson stick, and it doesn't need to last more than a single session.