I received a comment last week about how to keep a beginner violinist's left wrist from collapsing, and I was surprised to realize I had never shared this trick! It's pretty simple, and all you need is a rubber band (those are to violinists what duct tape is to everyone else!).
Pardon the blurry phone pics - I took these during nap time. Step one - put rubber band on the scroll:
Step 2 - slip student's wrist through the band.
It's important to make sure the band isn't too loose or too tight - just enough to give the student the feeling of pulling back slightly. Collapsing the wrist means the band feels tighter, so it's a good way to teach them to start noticing and correcting it themselves. If you have any other solutions for this very common issue, share away!