I have to say I don't have too many problems with fingernails in my studio. Generally, this is only an issue with new students. Once they are used to clipping their nails and how it feels when they play, they just seem to keep them short. I generally only need to remind parents once or twice. And for my students who are old enough to clip their own nails, I just hand them the clippers at the beginning of the lesson, if they forget during the week.
There are those who, in the past, have come in continually with long nails (long enough to click on the keys). I have tried everything....lecturing, reminding parents, phone calls, emails, parent conference, newsletters, posters....almost nothing will change the repeat offender.
My solution for long nails:
Immediately clip the nails of one hand only to allow them feel the difference as they play.
I don't mind doing this in the lesson. What could be done at home for free, is now costing the student approximately $1.00 per minute.
I've had 2 repeat offenders in my studio and its no coincidence that both were chronically poor practicers. Twice, I even had teens show up with acrylic nail tips! No kidding! In the presence of the parent, I offered a choice: 1. Cut them off right now and we will proceed with the lesson. or 2. You can go home without a lesson (or makeup or refund- that's my policy). Both cut them off.
Why does this happen? I think they just aren't practicing. How could they be with those nails? Because if they are practicing, its with dropped hand positions and flat fingers. And this is how some of them come to the next lesson- flat fingered. One of my students has been doing this for so long, I can't even correct his hand position anymore.
So this week, when he came (once again) with long nails, rather than handing him the clippers and giving him my 400th lecture and explanation of how this has negatively affected his hand position, I just clipped the nails of one hand and left the other. I then asked if he felt the difference. He said he did.