The emphasis on testing forces us to measure knowledge acquisition in the very short run. But more than that, you might have the information, but you are not prepared to use it. It's hard to assess someone at the point that is most indicative of whether they've learned or not.
Psychologist and writer Adam Mastroianni says our minds are like the keep of a castle protecting our deepest held values and beliefs from even the most skilled attacks. The only problem with this design for self-preservation is that it also can keep out wisdom that might be both useful and true. Mastroianni's summary of the problem is "you can't reach the brain through the ears." Listen as Mastroianni talks with EconTalk's Russ Roberts about the implication of this view of mind for teaching, learning, and our daily interactions with the people around us.