During his debate with President Obama last night, Republican presidential candidate Mitt Romney boasted of being governor of Massachusetts while the state was ranked best in the nation in education.

Romney is likely referring to the National Assessment of Educational Progress (NAEP) test, which the Department of Education uses to grade states based on student knowledge in reading and mathematics.

Indeed, Massachussetts’ ranking has been impressive, and it ranked first in the nation in 2005 and 2007 in math and reading scores for 4th and 8th graders, both years under which Romney was governor. What Romney didn’t note was that the state also ranked first in 2009 — long after he had left his position.

In fact, it was also that way before Romney ever became governor. Here’s a table showing NAEP scores for Massachusetts from 1992 to 2003, drawn from a UMass Amherst report by researchers Stephen Jirka and Ronald Hambleton (click on it to expand it):

As you can see, Massachusetts significantly outperformed the nation every year tested. Some of this has to do with the public policies followed by the state, but it also has a number of social benefits that boost its educational potential. That includes the lowest number of uninsured individuals and the second-highest per capita income among all states.

Can Mitt Romney really take credit for his state’s educational results when they were already high before he took office and remained high after? No, the most he can take credit for is not catastrophically ruining an already good system.