Everyone talks about high school graduation rates, but no one-including me–has any idea what they mean and what they really are.

We operate from the assumption that 100% of students “should” graduate from high school and excoriate the schools when the numbers are anything less. The assumption–which is wrong–is that we used to have high graduation rates but now we don’t. This is simply wrong. Over the course of the 20th century, graduation rates started from a very low point–less than 10% of young Americans finished high school at the beginning of the 20th century–and the rate rose steadily until it reached 50% in 1940. By 1970, it was 70%, and since then it has inched up.

Today, it is difficult to know what the graduation rate is because there are so many different ways of counting. If you count only those who graduate in four years, then it is about 75%. If you include those who graduate in August, after four years, it goes up. If you add those who took five or six years, it goes up more. If you add those who received a GED or some other alternate degree, it is up to 90%. (Aficionados of the issue can have fun poring over the latest federal data here).

These days, politicians play with the graduation rate to make themselves look successful (never mind the students). They lament the “crisis” in dropouts when they enter office, then crow at every uptick once they are in office to demonstrate “their” success.

Unfortunately, the pressure to raise the numbers typically overwhelms the standards required for attaining a high school diploma. When teachers and principals are sternly warned that their school will close unless they raise their graduation rate, they usually manage to raise their graduation rate without regard to standards. The usual gambit these days is called “credit recovery,” a phenomenon that was unheard of twenty years ago.

Credit recovery means simply that students can earn credits for courses they failed by completing an assignment or attending a course for a few days or weeks or re-taking the course online. As I wrote this week in Education Week, online credit recovery is typically a sham, a cheap and easy way of getting a diploma that was not earned. Students sit down in front of a computer, watch videos, then take a test that consists of multiple-choice questions, true-false questions, and machine-graded written answers. If they miss a question, they answer again until they get it right. Students can”recover” their lost credits in a matters of days, even hours. I wrote about online credit recovery as academic fraud in my EdWeek blog this week. Students realize quickly that if they fail, it doesn’t matter because they can get the credits in a few days with minimal effort. In this way, the diploma becomes meaningless, and students are cheated while the grown-ups fool themselves into thinking that they succeeded in raising the rates.

In this way, Campbell’s Law applies. When the pressure is raised high to reach a goal, the measures of the goal become corrupted.

The same number may be used either to bemoan a lack of progress or to claim victory. For example, the recent “Blueprint” created by a business strategy group for the school district of Philadelphia lamented that “only” 61% of its students attained a high school diploma in four years. At the same time, Mayor Bloomberg in New York City was delighted to report that the graduation rate was up to 65.5%, a figure that included summer school plus a heaping of credit recovery. The state of New York, which did not include summer graduates, put the actual figure at 61%, no different from the rate in Philadelphia. The state says that only 21% of students are “college-ready,” and the City University of New York–where most of the city’s graduates enroll–reports that nearly 80% require remediation.

So what is the real high school graduation rate? I don’t know.