Your point got a lot of downvotes so I'm jumping in-
Any intercession in that process is just plain ineffective, and does more harm than good in the long run.
Everyone else should know that this is gospel. There is a definite point in learning when extra or continuing help is actively harming the student. The charitable have a hard time seeing this. "But, I'm helping!" At the point merlyn describes, you aren't anymore. Everyone has to find that line for him/herself so I don't pretend to prescribe it but it is real and deserves consideration by teachers.