If you can identify the meaning of the word "prospered" within a passage, chances are you know more vocabulary than most American high school seniors.

The results of the national standardized vocabulary tests are in, and the scores are troubling -- but not unexpected -- experts say. Average performance on the U.S. Education Department's national exams was mostly stagnant at low levels between 2009 and 2011, and the highest performers lost ground during that time.