...and as part of your operational procedures you don't just have the plane automatically filled after each flight without knowing what the next load will be. Jeez, after a few demonstrations it's not that hard to get a student to calculate how much fuel they
A: Need
B: Can load
Where I first instructed we did the fueling ourselves. More accurately, the *students* did the fueling, under their instructor's supervision. After 1st solo they were allowed to taxi over & fuel without direct supervision. Can't recall that we had many issues with W&B in the aircraft.
Some larger students preferred to, or had to, learn in a C172, but most students were accommodated in the C152s.