Why is it important to teach proper terminology?
There are many reasons to valorize terminology within the context of your class, but one of the best is that terminology is empowering. Knowing proper terminology allows your dancers to not only function but achieve in a variety of classrooms, both at home and abroad. Through the universality of ballet terminology, your dancers will feel confident in both their understanding of the terms and their movements. From the littlest dancers who are excited to call out the proper terms as they move to the advanced student who tweaks his/her performance of a movement based on a better understanding of the term, all of your students will gain confidence through the inclusion of proper terminology.
Are there other benefits?
Confidence isn't the only reason to move proper terminology to the top of your priority list. Understanding how the definition of a term relates to the movement itself helps us to better perform the movement, and understanding the words will help your students become better readers and generally broadening your students' vocabulary outside the dance studio. (See my article "Move Your Body, Improve Your Brain" for a deeper discussion of how language compliments movement and vice versa). As someone who chose to take French because the ballet words were in French and eventually went on to earn a PhD in the subject, I have to point out that you might also inspire a lifelong love of foreign languages.
As your dancers get older, their understanding of proper terminology will also allow them to ask more pointed questions about certain steps and how to perform them and about daily class combinations.
At what age should you start?
No matter how old your dancers are, you should start from the very first day of class. I know this sounds daunting and you're more worried about establishing classroom rules and getting your littlest dancers over those first day bumps in the road, but you can use terminology to engage the dancers and keep them involved in the class. From day one, I ask the dancers to say my words with me. My two and a half year old dancers love to say "plié, sauté" while we do our sautés, and my advanced dancers immensely from being able to speak the combinations before doing them.
Here is a fun coloring sheet that I send home with my dancers in November. (Note: I did not draw this turkey. I found it several years ago in free clipart and here's the link to the free coloring sheet: http://theotix.me/turkey-color-page.html/free-printable-turkey-coloring-pages-for-kids-for-color-page)
Below is a link to my studio Blog that is more oriented toward parents and you are welcome to share either version on your own pages:
http://www.artistryhouse.com/news/2017/10/29/why-is-it-important-to-teach-proper-ballet-terminology