The
valedictorian of my graduating class made a
13 
on the ACT. She tried to study for the ACT. I mean seriously studying: reviewing textbooks and notes from ninth grade till summer before senior year. She worked herself into a total basketcase. In her mind, this was the biggest beat-all, end-all test in the history of the world. Some of the biggest loser dopeheads in school kicked her ass on the ACT.
Standardized tests are overrated and a horrible way to measure whether somebody really knows their subject matter. First of all, they are mostly multiple choice, and there are many studies that show that some people are naturally good at taking multiple choice tests.
Despite her first attempt she took it later with a more relaxed attitude and made a decent score. Nothing great, but decent. She wound up going to State, majored in Architecture, and wound up graduating with honors. Haven't seen her since, but have heard she is having a very successful career.
Test anxiety is also a real problem for some people. I work as a trainer for my company. All of our employees have to take and pass a basic math and blueprint test within four weeks of their start date before they are "officially" hired. Had a lady that I tutored that did very well in class; she had no problem working the problems and getting the correct answers in class, but she would make a "12" or a "27" on the tests. She was a good worker, so they gave her one last chance to pass the test, but first she had to take a one week math class from me. Again, she did well in class. I said, "Why are you here? You ought to blow the test away." She proceeded to tell me that when it came to tests she just went blank. I got permission to give here a "practice test" that really wasn't, but I didn't tell her that. I set it up as just a practice run at the "real" test that she would have to take tomorrow. She made a "98". When I told her she had just passed the real test, she almost passed out.