The high school class of 2012 has taken its College Board exams and the results are not good, showing the nation still hasn’t cracked the code of how to deliver a quality secondary education to large numbers of students from diverse backgrounds.

The story wasn’t much better on the local front. SAT scores dropped for both the Cobb and Marietta school districts this year. Figures just released showed the Cobb average edging down by two points to 1520, while Marietta’s score plummeted to 1459 from 1482 last year. The scores for both districts remained ahead of the Georgia average (1452), but only Cobb students bested the national average.

The results are dismaying because they come after a decade of No Child Left Behind. If that law forces teachers, as critics allege, to “teach to the test,” it is not this test they are teaching to.

The test is divided into three parts, critical reading, writing and math. A perfect score on each section is 800 — 2400 if the student aces all three. But mean national reading scores were 496, a 40-year low, 34 points below 1972. Math was flat at 514, roughly unchanged since 2007. And writing was 488, down nine points since that section was added to the test in 2006.

Over half, 57 percent, did not achieve a combined score of 1550, the level at which a student is deemed ready for college-level work. The results were even worse at ACT, the other major college entrance exam, where 75 percent of the students failed to meet the readiness standard.

Scores across every racial group, except those of Asian descent, have declined since 2006.

Educators advanced ancillary reasons for the poor showing: a record number of students, 1.66 million, took the test; 27 percent were from low-income families; 28 percent said English was not their first language; and one-third were from families where the parents had not attended college.

But overwhelmingly, the single greatest factor correlating to achievement was household income. Students from families earning $20,000 or less had a mean combined score of 1322. The scores increase in stair-step fashion with each additional $20,000 in family income. But the threshold readiness figure of 1550 wasn’t reached until household income approached $100,000. The mean combined score for students from families earning $200,000 or more was 1722.

This suggests that most of the much-discussed education reforms — more testing, stricter teacher evaluations, smaller classes, charter schools — might result in improvements, some of them perhaps significant, around the margins, but that one of the most effective reforms would be a rising and prosperity for all. Easier said than done, of course, and not likely to happen under the economic policies of the current administration in Washington.

The other missing ingredient in education improvement is an increase in the number of parents closely involved in their students’ education. Yet once again, that’s easier asked for than achieved.