Appeared as a 'low-tech' yet significant teaching aid in the modern classroom, the blackboard has greatly shaped the medium, space and pedagogy of school education. Over the past two centuries, 'blackboard' itself has also been constantly remoulded in terms of its colour, material and function, from the traditional black wooden surface to the interactive digital screen, which requires comprehensive investigations from historical, technological and educational perspectives. This essay synthesizes approaches applied in three dimensions. First is the material and technological aspect, tracing the transformation of such 'boards' from stone/wood to plastic/steel to digital/online forms and their functions extended; then it focuses on the etymological and lexicographical dimension, comparatively analysing the definitions of blackboard, chalkboard and whiteboard in the representative dictionaries; moreover, an educational perspective is employed throughout the whole investigation, especially on how the invention and involution of 'blackboard' shaped the class space, teacher-student relationship and subject pedagogy. Beyond the concern of technology, this essay reserves due attention to the epistemological issue in dealing with the presentation, transmission and acquisition of knowledge under different cognitive contexts.