Well I took the U.S. History Subject test in June 2009 as well and I scored a 660 so I asked the same questions and did a little research. According to collegeboard.com, the mean score for the U.S. history exam is a 597 meaning we both scored above average. Now normally that is a very good score if you are not thinking of an ivy league school. (I'm certainly not) But those schools want like 750's or higher. Overall, it falls in the 62% percentile which is very good. We did not do bad at all and I hope this helped!
