Summer…  Time to reflect, evaluate and to search for new ski teaching ideas…
The following came from a discussion about a guy who initiates turns by twisting from his shoulders.  The result of this, apart from being inefficient and really difficult to do in variable snow, is that his upper hand drops back.  It is a very clear and obvious movement.  He has been given a drill to work on keeping his hands up and forward.  The outcome is that when the conditions and terrain are perfect his hands don’t drop back, the shoulder movement isn’t so obvious (because the big signpost of the dropping hands is not there) and people watching are happy that he is fixing his problem.  Give him some variable conditions, however, and the problem is still very clearly there.
Whenever I look through books on ski technique and watch what other people are doing I am often amazed by the number of different drills and exercises there are.  Some are undoubtedly fool proof; however, there are some that I question how useful they actually are.  There are many drills that address the symptoms of the problem but not the problem itself.  These are the ones which make a problem seemingly go away when the student is concentrating and are skiing well-within their comfort zone but as soon as they are challenged the old problem comes back. 
For the guy above, first he needs to figure out why the turn initiation is not coming from closer to his skis and the snow.  Figure out the cause, find a way to solve that problem and I suspect that the hand dropping will stop without any extra thought.
How often do the drills address the symptom and not the cause?  There are lots of people who have learnt to mask their bad habits.  Even some people skiing at a very high standard can, if you watch them closely, have a sneaky shoulder drop into the turn, have a dodgy heel push at the end of a turn, ski on the tails of their skis and become increasingly out of control.  Over the years, they have done endless drills that have hidden the problems though have never actually made them disappear completely.  Then, on the days when they stop concentrating those issues are there to be seen.

Next time you are given or are giving someone a drill to do, have a think about really what it is addressing.  Is it for a symptom or is it for a fundamental problem?  Usually once the fundamentals are right the other unnecessary and inefficient movements are no longer there.