H/T PURE.
“A story Sunday about single-gender schools incorrectly stated that two Chicago single-gender charter schools reported 100 percent graduation rates. In fact, the schools had 100 percent of their graduating seniors accepted into a postsecondary institution. The Tribune regrets the error.”
Hmmm. How many graduating seniors do you suppose that might be?
Fred Klonsky 
And how many of their classmates as freshmen have disappeared by senior year?
Generally these are schools that require acceptance to a post-secondary institution in order to graduate at all, so that number is always going to be 100% by definition.