California ranks near the bottom of the states, along with Mississippi, Alabama and West Virginia, on the National Assessment of Educational Progress, the biennial  test in math and English language arts known as the “nation’s report card.”

So it’s hardly a surprise that students in Fresno Unified and Los Angeles Unified did  worse than peers in most of the 18 large urban districts that participated in a NAEP math study released this week. What’s disappointing is by how much.

Fresno’s math score of 219 for fourth graders in 2009 was higher than only two of the 18 urban districts (Detroit and Cleveland) that participated in the NAEP exam. Los Angeles, tied with Baltimore and Chicago with 222 ponts,  was not much higher. The average for the 18 districts, which included  New York City, Washington, Atlanta, Houston, Detroit and Miami, was 231; the national average was significantly higher – 239 on the 500 point scale.

Eighth grade results weren’t much better: The 258 points for LA and Fresno were behind 10 of the 18 – and far behind the urban average of 271 and national average of 282.

There was also good news. The 280 points for eighth graders in San Diego in 2009, the third California district in the study, was higher than the urban average of 271, right behind the national average of 282, and higher than every urban district except for Charlotte and Austin.  San Diego’s fourth grade scores were slightly above the urban average, with a score of 217.

Both San Diego and Los Angeles have seen their NAEP scores increase significantly since 2003; the average 10 point-increase for San Diego, including 16 points in eighth grade! — is twice the national gain.

Demographics can explain much of the difference. Urban districts have larger proportions of poor, minority kids, and both Fresno and Los Angeles top the 18 districts with highest percentages of low-income and English learning children. Next to Charlotte, San Diego has the least number of low-income students – 55 percent. States like Texas exclude more English learners from taking NAEP than does California, which can skew results somewhat.

But demographics are not destiny, and also can’t conveniently explain away the fact that white eighth graders in California  score below whites nationally, and white fourth graders in California score no higher than the national average.  The same is true for white students in Los Angeles and Fresno (but not San Diego). Even eighth grade Asian and Pacific Islanders in California, the stars of the state’s STAR tests in math, test below their ethnic peers nationally (294 compared with 300 for Asians nationwide).

So something else is happening – or not happening — in California. The problem is not California’s math standards, recognized to be among the most rigorous in the nation. But I’ve heard many teachers complain that the sheer number of standards they must charge through discourage teaching concepts in depth.  (The curriculum frameworks do place a higher priority on power standards.)

More likely, California’s low scores reflect a combination of factors: the challenges of teaching math to large numbers of poor kids learning English and teachers, particularly in late elementary grades, who are math-challenged themselves. They have trouble teaching concepts they don’t truly understand.

NAEP’s not the perfect measurement. It’s not aligned to California’s or any particular state’s curriculum frameworks. That’s one reason for the push in Washington for common core standards that make more accurate state comparisons possible.

But it’s the best yardstick available for now, and California’s low scores shouldn’t be laid on the backs of  kids of color.

(The National Assessment Governing Board, which oversees NAEP, produces reams of well-organized, interactive data that are worth exploring. Sacramento County Superintendent David Gordon is on the governing board.)