First off we are not talking about "some aircraft" we are talking abut the C 172.
First off what we are (or should be) be teaching is habit and habit for not just a C172 but for all aircraft that may be flown within the privileges of the rating.
The point that is sometimes missed is that you may want to isolate one of the fuel tanks in the air, if the fuel in that tank was contaminated for instance.
If a student needs to continually practice rotating it from the 12 o'lock position to the 6 o'clock position in either direction, than in order to get it right then he/she is not smart neough to be a pilot.
As i know you are smart 'neough' to be a flying instructor you must have misread what I said- I said," a first flight of the day" and I quote:
A first flight of the day check checklist should call for the exercising(not yet mentioned) of the fuel cock and the selection of all positions.
I show the student how the fuel selector works in the cockpit orientation at the beginning of the PPL syllabus.
Pointing out something once at the start of the syllabus is hardly 'best practice' flying instruction is it?
Of note Cessna's are supposed to have vented fuel caps on both sides. I occasionally see airplanes with only one vented cap or in one case a plane with solid caps on both sides . This can happen when caps break or wear out and are replaced with a "serviceable" spare
This is true for the C172 but the C152 is only required to have a vent cap on the right side