When educational statistics and state politics collide, the results can be cringe-inducing.

A memorable example dates back to March 4, 1999, when the governing board of the National Assessment of Educational Progress (NAEP) released the results of national reading exams. They showed that North Carolina was one of only five states that posted significant gains in 4th-grade reading performance from 1992 to 1998.

Not surprisingly, then-Gov. Jim Hunt released a statement and did a round of media interviews to celebrate the news. “We’re on the right course,” Hunt said, “because we’ve kept our focus on what works” — such as “making sure our children get a Smart Start.”

In his exuberance, however, the governor didn’t stop to do the necessary arithmetic. While his signature preschool program received legislative authorization in 1993, Smart Start didn’t reach a majority of North Carolina’s counties until 1996 and then went statewide in 1997. Unless the participating preschoolers became so brilliant that they immediately skipped several grades or started tutoring their older siblings, it was impossible for Smart Start to have affected the reading scores of 4th-graders in 1998.

I don’t recount this story to pick on Gov. Hunt. Many politicians fall into the same trap. Education is the single-largest category of state spending and a top priority for many North Carolinians when they cast state ballots. So politicians have a strong incentive to claim credit for positive news about education and shift the blame for negative news to their opponents.

But education policy isn’t so simple. By the nature of the institution, the benefits of even highly successful reforms take years to manifest themselves. Moreover, education reforms rarely get passed one at a time. They come in clumps. In the mid-1990s, for example, North Carolina lawmakers not only created Smart Start but also rewrote part of the state curriculum, instituted new standardized tests, authorized charter schools, and changed teacher-compensation policies. So any subsequent gains in student performance could have multiple causes (including non-policy factors such as in-migration from other states).

To make things even more complicated, the yardsticks for measuring student performance kept changing. North Carolina’s end-of-grade and end-of-course tests proved so problematic that they were repeatedly re-jiggered and eventually abandoned. The proportion of students taking NAEP exams changed, as well. And North Carolina stopped reporting a ridiculously high 96 percent graduation rate in 2004, adopted a more sensible cohort measurement, and then saw graduation rates rise from 68 percent in 2006 to nearly 83 percent in 2013.

So establishing valid relationships between education reforms and education outcomes is extremely challenging. The task doesn’t lend itself to self-serving rhetoric or political gamesmanship.

Consider that recent rise in North Carolina’s graduation rate, for example. Democrats have claimed that it proves the value of past Democratic policies, including Smart Start and More at Four. Republicans have claimed that it proves the state budgets they fashioned in 2011 and 2012 did no significant harm to public education, as their Democratic rivals had alleged.

The available data just don’t offer a comprehensive explanation for the trend. Remember, North Carolina education doesn’t operate in a vacuum. Other states have experienced large gains in graduation rates, too. When Education Week used comparable data to track changes in graduation rates by state from 2006 to 2010, it found that North Carolina’s gain of 8.4 percentage points did beat the national average gain of 5.5 points. But so did the gains in Alabama (8), Georgia (8.1), Virginia (8.3), Texas (9.5), Tennessee (10.8), and Florida (15.4).

Unless former North Carolina preschoolers have fanned out in massive numbers to populate public schools in other Southern states, it would be odd to credit Smart Start and More at Four for what is clearly a broader trend — one that quite possibly reflects the benefits of No Child Left Behind for disadvantaged students and the crushing effect of the Great Recession on teen employment, which may have discouraged students from dropping out of high school to enter the job market.

Education will always be a political issue. Still, let’s hope that politicians graduate to a higher level of political discourse about it.

Hood is president of the John Locke Foundation.