From my college classmate Zeke Emanuel in The New Republic, here. Money quote:
Done properly, testing is not inert. Rather, it can be much more like the physical phenomena underlying the Heisenberg Uncertainty Principle. In the act of measuring students, you can actually affect how much knowledge they absorb and how well they retain it.
Zeke is raising a really important point. Learning outcomes are improved by the action of taking a test and getting the feedback of a grade. And increasing the frequency of testing actually improves those outcomes.