Some modern classes do not have grading or even a methodical syllabus.Students just turn-up and train whatever they want.
This is bizarre.
It goes against virtually every teaching model practiced in the world today; whether piano, maths, reading or a martial art.

e.g. A child starts school with rudimentary language skills and they are taught the alphabet, then spelling, grammar etc.
This process continues throughout their entire education; the layering of skill, the exploration of the nuances.
No child starting school is capable of discussing Dostoevsky with the teacher.

Learning must be incremental and progressive.
You cannot just 'pick and choose' what to learn in an internal martial arts class.

The art is way too complex to be approached haphazardly.