The main difference comes from different counts of students who should have graduated each year:
There's also a difference in counting total graduates that looks like this:
Combining the two results, the Department took a slower-growing graduate count and divided it by a faster growing potential-graduate count--and the result showed 2009 results as weaker than 2008. I saw more graduate growth and less potential growth--and my results showed 2009 as stronger than the year before.
Note to the frustrated: Would it be better to divide graduates by the number of students who started grade nine four years earlier? Yes, of course. Doing it that way, though, depends on a student data system that assigns each student a unique identification number and then tracks each one, including each one who moves to a different school. We've been talking about that approach at least since 1999, but we didn't get it fully launched until the fall of 2009. It will take four years for that system to track its first ninth grade through to graduation, and then debates like this can finally come to a close.