recruit, enter, enrol, inscribe, inroll, register, enlist, enregister, list, enrank, more...

drop out, withdraw

sign up, join, register, apply, be admitted, more...

many, poor, total, few, high, public, primary, secondary, physical, average, black

sign up for,   join a group,   sign me up,   take a class,   take in a course,   to register,   take a course,   "sign me up",   to take a class,   take courses