I talk a lot with my students about the idea of practicing perfectly. Don't repeatedly practice mistakes, but, practice your repertoire perfectly and as slow as necessary to play it perfectly.  The following article discusses the notion of 'deliberate' practice and how it affects high performers and achievers.

www.businessinsider.com/anders-ericsson-how-to-become-an-expert-at-anything-2016-6
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This is a great perspective on the make-up lesson.  Many teachers choose to offer make-lessons but this parent/author of this article opposes this practice. Read the article below to find out why!

http://ottawasuzukistrings.ca/makeuplessons/