By completing all given homework and assignments, students will be well-prepared for their tests. Simply doing one's work as assigned is enough. It is the best study method because it reinforces what one learns during lectures in class.
Completing all homework and assignments is not enough. Although it does help reinforce learning, there is a distinct difference between homework and studying: Homework is for extra practice, and studying is for internalizing and mastering content.
[P1] Completing all assignments is the best way to study.
Rejecting the premises
[Rejecting P1] Homework and studying is not the same thing.