A chalkboard is a block that can display text rather than using a sign. There are three available sizes:
Slate Poster Board
They are obtained by selecting from the inventory when in creative mode or typing the following commands into the chat:
Slate 1 x 1
Poster 2 x 1
Board 2 x 3
Chalkboards can be placed onto most blocks to appear as if they are fixed to a wall or standing on the ground. Once you have entered your text, you can choose to lock it to prevent editing. You can choose to include a blank chalkboard to encourage students to type their answer or understanding of a topic.