Workers pulled the old boards off a classroom wall in Oklahoma City and found another blackboard hiding behind them.
Nobody had wiped it since 1917.

It happened in June 2015 at Emerson High School, just north of downtown. Contractors renovating the building took down the smart boards and bulletin boards. Behind them were green chalkboards. Behind those were slate blackboards, still covered in chalk.

The lessons were intact. A teacher's perfect cursive. A multiplication table drawn as a wheel. Music notes. Spelling words. Children's names. The principal wondered if they were up there for being good, or for being bad.

And it was right after Thanksgiving. In every room there were turkeys and Pilgrims. On one board a little girl in a pink dress was feeding a turkey, next to a calendar for December 1917.

One board was dated December 10, 1917, and signed "Miss Walker's Room." Another was signed by the school custodian.

America had entered the First World War eight months earlier.

"You would have cleaned off your board so you could be ready the next day to come back and teach," said Sherry Read, a math teacher at the school. Nobody knows why these were never wiped. At some point newer boards and walls were simply put up over them.

The principal said it felt like walking into a time capsule. The district voted to cover the boards again to protect them, and in January 2016 workers found more boards from December 1917 behind other walls.

The children who drew that turkey would be more than 115 years old today.