I wasn't aware that a GPS was manditory equipment in a FAA ppl training aircraft.
I am sure its the same in the UK that if its fitted the student is taught how to use it (never flown a school machine with it fitted to be honest). But in both cases I should imagine that the standard of training and best practises is in the hands of the instructor.
In both cases an old hand hairy arsed GA pilot will give quality instruction which will guard against fixation and duff in equals duff out. And a zero to hero cluless wonder will be the blind leading the blind.