via OKCPS@twitter

Contractors in Oklahoma City were removing chalkboards from a public high school in June in order to put up new smartboards. Then they discovered a little piece of history. Hidden behind the recently used classroom boards were another set of amazingly well-preserved chalkboards—complete with lessons on Pilgrims, multiplication tables, and a countdown calendar to Thanksgiving 1917 (though the calendar is curiously labeled December, with only the first row of dates changed to reflect the new month).

See the full gallery at The Oklahoman

Apparently preserved by the school's custodians, the boards were signed and dated between November 30 and December 4, 1917, and then the new slate blackboards were installed on top of them. Colorful drawings of a turkey, a schoolgirl blowing bubbles, and ships sailing on the ocean remained intact, as did a music staff with "do, re, me" written over it, and an old, unofficial version of the Pledge of Allegiance. Even an old wheel method of teaching multiplication, which the high school's current principal says she's never seen before, was on the rediscovered boards.

See more photos at TheOklahoman.com.