Lower body drills
 

I have two students who start out with the correct downswing sequence, then the hips stop rotating and remain somewhat square through impact.

Does anyone have any good drills for this problem. ;

Thanks

How about Tom Tomasello's extensor action drill? It does all 3 zones. It can be seen on the drills chapter of his videos in the gallery section.

Essentially, have them set up in a 3 point stance. Make a fist with the left arm and grab the left arm at the wrist with the right hand in a golf posture. Do a right forearm pickup to the top, then swing through to finish.