Changing basis is a common task when solving quantum mechanical problems.  As part of a research project investigating student understanding of basis and change of basis in quantum mechanics, we developed a tutorial to support students in learning about basis in the context of spin-1/2 systems.  We have since created an interactive online version of the basis tutorial as part of a freely available suite of online quantum tutorials called ACE Physics (https://acephysics.net).  The ACE Physics tutorials include dynamic guidance elements and, unlike other tutorials, are intended for use outside the classroom without instructor facilitation.  After extensive study in an instructor-supported environment, we assigned the ACE Physics basis tutorial as homework in two semesters of upper-division quantum mechanics, and we report on the effectiveness of the activity based on pre-/post-testing and comparison of student exam performance with a similar semester that did not include the activity.  We find that the tutorial produces sufficient learning gains to justify continued assignment as a homework problem in our classes.