Read a book by James Loewen titled "Lies my teacher told me." Actually, you only need to read a few pages regarding Washington Irving, the author or Rip Van Winkle and the Legend of Sleepy Hollow. Irving wrote a book in 1828 titled "The Life and Voyages of Christopher Columbus." In this book, Irving, which was largely written as a joke, indicated that Columbus set out to prove the world was round. This is utter nonsense. No one at the time or any time previous actually believed the world was flat. Nonetheless, Irving's work of fiction was regarded as truth by some, and somehow made its way into school history books.
I recall in the 6th grade seeing a drawing in my social studies book depicting Columbus sitting on the shore, watching ships come over the horizon, and determining for himself that the earth had to be round. He therefore set out to sail around it to prove his theory. If you ask any grammar or high schooler, you'll likely get a similar answer to the question as to why Columbus sailed in 1492. This is rubbish.
So, you all owe your silly flat-earth beliefs to a work of fiction written by Washington Irving. Ironically, Irving even admitted at the time that it was a joke, but many took it seriously anyway, just as you do now.