Extracurricular activities are mandatory in the Yumenosaki idol course. Every student must be in one club, but joining a committee is optional. All clubs must have at least 3 students, or it will be dissolved. The exception to this is the Ninja Association, due to Mao Isara, the student council secretary, vouching on its behalf.
Clubs allow students to hone their skills and form bonds with students who share their same interests. Committees are a way for students to get involved in the hands-on work related to idol performances, as well as make connections within the industry related to that committee's field.
Clubs were originally voluntary. However:
The year before Ensemble Stars! began, Eichi Tenshouin used his authority as student council president to make club participation mandatory. He desired to exhaust and overwork the Five Oddballs by forcing them to participate in both club and idol activities at once.
There is no indication Eichi ever rescinded the rule that club activities are mandatory.
See the Yumenosaki Private Academy page for more information about school life in Yumenosaki.