A mobile classroom blackboard supported by a wooden trestle. The schoolteacher would write on the surface of the blackboard with chalk to explain a lesson to students. It was a fundamental tool for teaching in schools. The schoolteacher or professor would write or draw information on the blackboard to illustrate their explanations, and in this way the students could follow the lesson more easily and copy what the teacher had written. This piece is from the School of Sinués in Huesca.