My OH had a go at lunging my 4 year old last weekend. He didn't do too badly, apart from being a bit whip happy. (Had to remand him its not necessary to keep signalling with the whip, definitely not necessary to wave the whip when asking for a slower pace, poor confused horse).
He handled the horses freshness well better than I sometimes do and got him going round nicely on the right rein.
When it came to changing to the left though he had problems (horse is an arse about changing directions, he takes it as an opportunity to test you).
I stepped in and finished because I couldn't explain to OH what to do, even though I can do it myself.
So, if you were teaching someone to lunge, how would you explain how its done and what to do to send the horse out, and what to do when the horse plants its feet when changing direction, and generally acts like a nob and tries to intimidate you?
I never have problems myself but just can't put into words how its done!