fully agree with those.
teach rolls and loops ASAP
the reason being is it breaks up the boring circuit flying and keps the brain alert, it also teaches them how to recover, any posistion the plane is in, is mearly a roll or a loop half way through or combination of the both, once they get this, they can recover from most tricky situations quickly. ( if not waiting till the last moment teaches well too )
I dont load them up with silly hints, like propping up the wing with the stickwhen your comming towards your self, this confuses, and slows down reaction, it may take a little longer to get it, but it'll click quicker and become more instinctive, afterall we all look in the mirror and cope ok.

heres by biggest trick, it sounds very weird but stick with me.
Before you sleep you have about 30 mins where you lay there thinking of nothing, this is the perfect time to fly, imagine your holding the transmitter and fly the plane, throw in some wind, some landings ect, your brain will do an amazing job with this, best of all you sleep with this as your last learnt lesson and it will stick. i improved amazingly fast after i started this.
its also well know if you learn one thing in a day, then try to learn something else, you'll forget some of the first, so try to make learning the only big thing you do that day, also practice just one thing like landings for a day, before moving onto something else the next day/week