I wish the author had been more clear here and cited his statistic, but he's mostly right. The report "High School Dropout and Completion Rates in the United States: 2007" (http://nces.ed.gov/pubSearch/pubsinfo.asp?pubid=2009064) has a graph showing that the middle income dropout rate is about the same as the overall rate. The upper income students make up for the lower income ones. And according to the report at http://www.americaspromise.org/Our-Work/Dropout-Prevention/C... "Nationwide, nearly one in three U.S. high school students fails to graduate with a diploma."