In the 2008 campaign when Barack Obama pledged to improve high school graduation rates, it seemed to us that it would be an easy figure to check down the road.

Of course, all one would need to do is compare graduation rates before he took office and at the end of his first term. Then we would give him a grade on his progress

Not so.

As it turns out, all we know is that the graduation rate appears to have improved between 2007 and 2009, which says nothing about changes under the Obama administration. But we'll get back to that. First a little background:

Obama promised to improve the high school graduation rate because the Organisation for Economic Co-operation and Development -- better known by its acronym "OECD” -- had been publishing annual reports saying the U.S. was in the bottom third of its list of 26 countries in high school graduation rates, behind Korea, Slovenia and the Czech Republic.

So Obama committed to both improving high school graduation rates and improving the country's performance relative to other countries.

As president, Obama embarked on an ambitious education reform package through the Race to the Top competitive grant program, which leveraged $4.5 billion in potential grant funding to get states to make changes, such as allowing charter schools and tying teacher evaluations to student test scores. One of the program's goals was to improve graduation rates.

But we aren't likely to know how Obama has helped or hurt high school graduation rates for several years to come. And even when the data becomes available, some will inevitably dispute the statistics as accurate measures of high school graduation rates as well as their comparability with other countries' graduation rates.

The entire notion of a high school graduation rate is complicated -- there are a handful of ways to calculate high school graduation rates depending on how you count substitute certificates and degrees, transfer students, and the length of time it takes for a student to graduate. Even in 2012 not all states use the same methodology for tracking graduation rates.

The U.S. earned a world ranking of 21st out of 28 in high school graduation rates in the OECD's latest report on global education based on 2009 data. It's worth noting that this represents the number of people who graduated as a fraction of the total number of people who were old enough to graduate that year in the U.S. That may be a good indicator of what percentage of our population graduates high school, but it doesn't say much about how high schools perform in retaining students through graduation.

Another statistic also reported by the OECD called "upper secondary completion rates” shows that the U.S. is second, behind only Ireland, when you look at graduation rates among students who were enrolled in high school in the 9th grade. We asked Dirk van Damme, an education analyst with OECD, why the U.S. is so much higher on one list than the other. He said many U.S. students drop out before high school, so they don't count against the completion rate.

The latest figures we have about U.S. high school graduation rates comes from the Education Department's National Center for Education Statistics. The center calculates something called Averaged Freshman Graduation Rates for Public School Students, which is an estimate of the number of students who started as freshmen and finished high school within four years (in public school). In the 2008-2009 school year, the U.S. graduation rate was 75.5 percent, up from 74.7 percent the year before.

An education think tank called Editorial Projects in Education uses a separate calculation based on federal government data, which also suggests that high school graduation rates are getting slightly better. The research group said the 2009 graduation rate was 73.4 percent, up 1.7 percentage points from the year before.

Chris Swanson, who oversees the group's research on graduation rates, said we can't know if Obama kept his promise, even with the 2009 data.

"Those would be graduates from the school year that had already started when Obama was elected – not really enough time to judge the administration's impact on graduation,” he said.

This year all but two states have adopted a national standard for counting high school graduation the same way. That means we'll be able to assess the next president's record on high school graduation in ways we can't with Obama.

Since national data for high school graduation rates aren't available for 2010, 2011 or 2012, we'll leave this promise In the Works.