Answer: blackboards

AnswerCrossword Clue
BLACKBOARDSSchoolteachers' surfaces
blackboardsBLACKBOARD, a hard smooth usually dark surface used esp in a classroom for writing or drawing on with chalk
blackboardsA large board with a smooth, typically dark, surface attached to a wall or supported on an easel and used for writing on with chalk, esp. by teachers in schools