Bob - I would say that the answer lies in the integrity of the individual instructor.
If the "student" is a licensed pilot and is current on class, medical etc. then there is nothing to stop somebody riding along as a passenger.
If that passenger just happens to fully understand (does anybody
) the workings of the ADF then there is nothing to stop them passing on that knowledge....maybe with an intercept or tracking excercise or two.
If the pilot is NOT logging that flight as training specifically towards a particular licence or rating then they do not NEED to log it as Pu/t.
It really depends if the instructor is hour building at the expense of the "student" or is genuinely interested in helping the inexperienced pilot to progress.
If somebody wants to get paid - which is not unrealistic considering the cost of gaining their ratings - then charge them for good groundschool, and it should take away any aerial work argument of having a qualified flight instructor on board.
BTW - NO, you would not be able to log it as well. That's what I mean about the "hour building instructor".