The Flying Instructors' Group of the Honourable Company of Air Pilots (formerly GAPAN) has produced guidance material for flying instructors and made it available on their web site https://www.airpilots.org, through "aviation matters" and "flight instructors". Their PPL Flying Instructors Guide, was written in conjunction with members of the staff of CFS Cranwell and examiner staff of the CAA to assist graduates of flying instructor courses, but can be useful to any instructor.
Thanks Thomas! I agree it's a good idea for VP propellers. However, the guide states at the beginning it is written for training in aeroplanes with fixed pitch propellers. We didn't want to get tied into discussing variations for more complex aircraft. Best wishes,
David