This week my students were trying to explain the relationship between the diagonals of a rectangle and square. They said things like - they are both 13.5 inches or they are the same thing, so I asked them to find a word on the word wall to describe the relationship. They quickly picked out congruent. It just so happened that I was being observed by a district specialist at the time and he said it was the first time he had actually seen a teacher use a word wall in instruction.
At my school, the word wall is one item on a long list of required elements for dour classroom. Mine is completely student driven. They write the word and create a picture to go with it. Sometimes they choose to create a Frayer model or write a short definition. Sometimes I ask a student to add a word to the word wall and sometimes they initiate it themselves. When the students are involved, they take ownership and this word wall becomes a great resource to them.