If students graduated from high school in 2012 at the same rate that their predecessors did in 2001, 1.7 million fewer students would have received diplomas. That the last decade or so has seen such tremendous progress in graduation rates is a triumph. Even better, the improvement itself offers insight into producing even better results.

"It's actually a story of remarkable social improvement, that you could actually identify a problem, understand its importance, figure out what works and apply it and make a difference," said Robert Balfanz, a researcher with the Everyone Graduates Center at the School of Education at Johns Hopkins University. He was an author of the report that verified that the national high school graduation rate had reached 80 percent, and projected that it would reach 90 percent by 2020.

Most of the progress has occurred since 2006 and has coincided with specific policy aimed at diminishing dropout rates. Those initiatives included closing or improving schools that had been identified as "dropout factories," so that the number of them declined by 32 percent in six years. Other successful methods included one-on-one interventions with at-risk students in many districts. Most encouraging is that graduation rates increased by 9 percent for African-American students and 15 percent for Hispanic students.

The authors recommended broader adoption of methods that were used in the states that made the greatest progress. And, they recommended concentrating those efforts in big cities where dropout rates remain high.

Over time the higher graduation rates themselves likely will produce more progress because they will help to mitigate economic disparities that help drive the dropout rate.

The statistics are encouraging, but even more so is what graduation means for the millions of students who stay in school. As the study predicts, the trend should inspire further progress.