I teach math classes that do not fit nicely into the courses as presented on Khan Academy. In the first months of school I have assigned to the same group of students practice from Math 8, Algebra 1, Algebra 2, Math 6, and Pre-Calculus. I have not once assigned the entirety of content covered in a quiz or a test, so I am not able to get any value out of the quizzes or tests.
What if teachers could create their own quizzes or tests, not that they would necessarily be called that, deciding from which practice sets to pull questions? Perhaps it could be called creating a Mixed Practice assignment. I see two immediate benefits. First, I would be able to actually leverage quizzes and tests for the benefit of my students if I could tailor them to contain the content I covered and only the content I covered. Second, I could create assignments that cover content from different courses to better provide opportunities for students to practice and review.