quite a challenge for any partner to teach the other.
Which goes something like this in my experience:
"but we're different than other couples..." Yeah right we are

. Oh well. In my case, she, did learn to ski and is still working hard at getting even better; quite the trooper putting up with me on a number of occasions.
Do any of you take lessons, clinics, view how-to videos, even if you are an advanced skier?
I am in a unique situation as a coach and (now ex-) racing program director. Far more often I'm the one giving clinics and advice to others (at all levels). I try to let friends just be, unless they specifically ask me to give them pointers. Still it's a very challenging job to teach people or kids in the correct way to get good results without pushing too far or etc...
And for myself, far too often others assume I already know everything, even though I love getting constructive feedback and on certain video taken of me I will analyze frame by frame what I am doing and could/should be doing differently (though getting video used to be very rare until last season when the coaching duties diminished). And even though somewhat out of the coaching biz now, I've been lucky to stay involved in at least one clinic per year - albeit not having to drop cash to do so given my connections to the race team.
Unless a true beginner, I wouldn't recommend a group lesson. A specialty clinic at local mtns are usually rather good for many folks. Otherwise best bet is to find a way to pay for about one hour of private or nearly private instruction. The instructor gets to see your skiing for just long enough that by the end he'll have 2-3 tips/drills for you to try and you can practice them on your own instead of continuing to pay someone just to look at you and tell you the same thing over and over.
Kids, the group dynamic/camaraderie I find is a critical aspect, so especially development (Devo) level of race teams are usually a reasonably priced option for dramatic improvement IMO (then wait to see if the racing part is really their cup of tea - at least in the meantime they get great instruction and huge improvement as well as many life lessons out on the hill).
Big topic (at least for someone like me) and I could drone on, but won't (esp cause I know that I don't know it all).