HI! I also had some of my students doing this. Try bringing in a mirror to show them that a mirror copies gestures but then show them that you are talking to the mirror and the mirror is not echoing because it cant do that. Practice 'mirror' with them for a while and use'repeats' in your lesson sporadically. When it wont be too many, they'll probably distiguish it easier from one another. As you go on, continue adding a few more repeats until they learn to look out for it and do it automatically. Good Luck!!!