For a while I have been asking my students to film the pieces they are playing and to send me those videos between lessons - specially when we don't meet every week.
It helps very much - in the same ways an audio recording helps, plus a few more:
1) If it's a new song, I can note-check their performance easily while it's stil slow, before any mis-readings become mechanized. Also the rhythm.
2) Body tension is very clear - you can say "at 2 minutes and 13 seconds your right shoulder locks up in anticipation of the arpeggio section - practice getting there, stop, relax, and continue."
3) It keeps the student accountable between lessons, discouraging cramming.
4) It is a brutal reality check that can be done privately - it all but eliminates the tendency some students have to play material that is too difficult too soon.
What else? Any ideas?
I am just making the transition from recording to filming my own practice - I'll post my ideas as things work out.