Last year (on a cart) I glued the words "Word Wall" on the top of a
piece of poster board and laminated it. It was then brought along
from class to class with my other visuals. I would write vocabulary
words on strips of paper and tape them onto the word wall as we
learned them.
Most of the classrooms I taught in had magnetic chalkboards so my
visuals would just go over whatever was already on the boards.