All students of the secret CareFree school in DGSD had to be beautiful. How on earth do you pick students when they are young. Beautiful kids dont always become beatiful adults. Do the schools pick them when they are in their teens? Doesnt sound likely. I know that this isnt the only requirement, but it must be important since WZT to hesitate to take on ZX as a student.
And I dont know if it is a requirement for the Tomb sect, but all their students were beauties! Even YG!