The old blackboard was uncovered in the school's G Block of classrooms, which is close to the Browne Street side of the school.

Forbes Public School Principal Meg Staples said they believe the old blackboard with the lesson dates back to the 1980's.

This block started off as Forbes Public School's main office area before being converted into classrooms in the 1950's.

Ms Staples said the school is steeped in a lot of history, and it is nice to find pieces of it tucked away around the school.

If anyone knows or remembers more details about the lesson lost in time get in touch by emailing brendan.mccool@forbesadvocate.com.au