Here is a Cultural Literacy worksheet on the idiom “tip of the iceberg.” This metaphor remains in sufficiently common use, I think, that students, especially students for whom English is a second language, might want to learn it at some point. This is a half-page worksheet with a reading of two compound sentences and three comprehension questions. With characteristic brevity, the authors of the passaage (i.e., the authors and editors of the The New Dictionary of Cultural Literacy) convey that this idiom indicates “Only a hint or suggestion of a much larger or more complex issue or problem.”
If you find typos in this document, I would appreciate a notification. And, as always, if you find this material useful in your practice, I would be grateful to hear what you think of it. I seek your peer review.