During classroom discussions, my room used to sound a lot like this:
Me: What do we know about these angles (points at a set of vertical angles)
Me: What do these two angles share?
Student A: A point
Me: Great! Where is that point located?
Student B: Where they cross
Me: What is that point called?
The "discussion" would go on from there with me asking ever more information loaded questions trying to get the students to the point that the angles were vertical and therefore congruent. It seriously made me doubt my teaching abilities. Until the day that a light bulb went off in my head that is. I realized that their lack of ability to answer my question had less to do with an understanding of the concepts and more to do with the fact that they lacked the language to express themselves mathematically. I sat down that evening and made a list of all of the vocabulary that was new(er) to that unit. Terms that they might have heard in passing or ones that I might have used, but not ones that they had ever really practiced. I came up with almost 40. I was astonished so I went back through the unit I was teaching and double-checked. Nope, no mistake, it really was almost 40. The next day I went into class and gave them five of them to define as bellwork. The majority were able to give me two. At that point I felt like I was in an old space movie - you know: "Houston, we have a problem"...
As any good teacher does, however, I took the problem as a challenge to be tackled, addressed and fixed to benefit my students. Out of this problem was born a simple solution - vocabulary assignments to launch each unit and periodic vocabulary quizzes through each unit.
The vocabulary quizzes that we do through the unit vary. Sometimes they are matching with the definitions in one column and the terms in a second. I also give them quizzes where there are paragraphs to fill-in with words from a word bank. The hardest version, and the one that I tend to save until towards the end of the year, are the ones where I just give them the definition and they supply the word without being given a vocabulary list or word bank. I find that as the year goes on, their scores on the quizzes get better and better.