I got this visual teaching tip from watching my ballet teacher's preschool and Ballet 1 classes.
Her class was practicing tendu and the students had very slow and articulate feet during their parallel (preschool) and turned out (Ballet 1) tendus! After class, I asked what her secret was and this is how she teaches tendu:
1. Take out your imaginary piece of gum and chew it up so its really sticky (in the preschool class, everyone gets to say what flavor/color gum they are having)
2. Take out some of your sticky gum and put it under your toes! (An explanation of why we only do this with imaginary gum and never at home is also given at this point)
3. With straight legs, try to slide the foot out... but the toes are very hard to move! Finally we get all the way out and the gum pulls us back to the starting position. Repeat while teacher says "sticky sticky (foot slides out) tendu (close)!"
4. Repeat with the other foot.
As they progress during the year, the teacher only needs to say "sticky sticky tendu" and the students recall the sticky sensation and slow down while pushing through their toes. I think this imagery would also benefit older students - after all, who doesn't love a little silliness in their class every now and again?
Hope it helps you or your classes! What teaching tips do you have for tendus?