The youngster had been mocked by classmates for saying he'd met the 16th president with his father, a journalist. His teacher wrote Lincoln to uncover the truth.
Instead, the president wrote to the boy: "Whom it may concern, I did see and talk with master George Evans Patten, last May, at Springfield, Illinois. Respectfully, A Lincoln."
The Raab Collection is offering the letter for $60,000. Vice President Nathan Raab says it's the only known surviving Lincoln letter written to a child.