A Class 4 instructor (brand new instructor) must operate under the supervision of a Class 1 or 2 instructor, but a Class 3 or up may freelance. You may not freelance on your own a/c: you must be at "arm's length" from the a/c. So you can freelance on a student-owned a/c, or one the student has rented from someone else.
Some flying schools allow a class 4 instructor to effectively freelance, finding his own students and settign his own hours, under the supervision of the school's class 1.