I'm more a drop in fan.... doing courses is too limiting and sometimes anyway you might want to go more than once a week!

A thing everyone does in Paris though is class passes, like buy 10 classes in one go... it ends up a bit cheaper and keeps you loyal

Same here in Milan, they run courses from Sep to Jan and Feb-June.

It's very rare to find a drop-in school over here, and it seems to work , considering the good numbers they gather every semester.