background board chalk chalkboard classroom communication dirty education green green board green chalkboard grunge grungy learning school schoolboard smeared surface teaching texture vintage wiped blackboard college presentation university 1 2 3 arithmetic blog class learn list math numbers one outline point points rules teach teacher three to-do two banner chalks copyspace educator illustration isolated lecture lesson object professor study template wisdom wood alphabet bill of fare black bulletin-board letter letters market menu notice-board restaurant sell write apple book books concept homework lessons pen pens schooltime discipline pupil pupils student students studies Africa America Asia Australia earth europe geography global history international journey land map planet travel World abstract advertisement advertising backdrop billboard blank copy space empty nobody old space symbol textured used back classes desks high school September textbooks