According to most recent data, which should have been available to Kerry staffers...
http://nces.ed.gov/pubs2006/2006601.pdf
The actual stats are 73.9% of freshmen graduate....
"The [averaged freshman graduation] 2002-03 national rate is 73.9 percent.
In summary, close to three quarters of freshmen nationwide graduated from high school on time in these 2 years (tables 1 and 3)."
And the title of that little document is:
The Averaged Freshman Graduation Rate for Public High Schools
From the Common Core of Data School Years 2001-02 and 2002-03
http://nces.ed.gov/pubs2006/2006601.pdf