A couple of years ago my daughter (six at the time) and I were about to finish a jigsaw puzzle when I held up a piece and said, "Yay, second to last piece." Her response: "You mean the penultimate piece, daddy." I bring this up not to brag about my daughter (alright, maybe a little bit), but to illustrate the impact of adults using the same words (PG and below, of course) with kids that we use with each other.
It's especially important to do this with children whose vocabularies are underdeveloped. Unfortunately, it's common to think you need to talk down to these students' levels rather than risk talking over their heads. That's what I thought until I realized the real risk was allowing the gap between students' actual and potential vocabularies to widen.
And so, just as I committed myself to immersing students in content-specific language (see Academic Fluency: A Key to Academic Proficiency), I also did this with everyday conversational language. And what I soon learned is that "adult" vocabulary isn't over students' heads after all. In fact, students often figure out the meanings of new words from the context in which we use them. And when they don't, you can often compensate by following the new word with its definition or a synonym. (I'm reminded of a third-grade teacher describing a character as "modest--you never hear him boasting or taking credit." And it was clear from students' responses to the teacher's follow-up questions that they understood "modest.")
There are, of course, many other strategies for developing students' vocabularies. But the one thing in my experience that transcends those strategies is talking to kids like you talk to adults. Do this, and you'll do for your students what my wife does for our kids. (You didn't think my daughter got "penultimate" from me, did you?!)
Join my mailing list for announcements about webinars and the work I do to improve teaching and learning.