Steady on with the Cessna abuse!
My Cessna has bang on accurate fuel guages that are verified by a very funky FS450 fuel computer.
I know exactly what my plane uses at any flight condition and plan accordingly.
But the fact is that most instructors that I have come accross know squat all about fuel consumption and planning let alone leaning. It is true that they jump in fly the required lesson and jump out, nothing is ever taught about leaning and consumption other than some arbitary figure bandied around the school.
My aircraft uses 33lph at full tilt in the climb, 23lph at 105kts and leaned back which I do once staright and level above 1500ft it does 19lph. The change of prop from mcauley to sensenich was the most enlightening thing to happen to me in a ong time!
I was not taught this by an instructor despite flying one of the most common trainer aircraft on the planet, but by several hundred hours of watching the guages and dipping the tanks.