What caused the uptick in Minnesota graduation rates?

Did a larger percentage of Minnesota high school students graduate on time in 2013 because of improved performance in the classroom, or simply because previously required tests were scrapped?

Last week, the Minnesota Department of Education reported that 79.5 percent of the state's high school students graduated on time in 2013. By MDE's calculations, that's the highest grad rate since 72 percent earned diplomas in 2003.

The latest grad figures also showed across-the-board improvements among white students and students of color — even though minority teens still lagged their white counterparts substantially.

Improvements are certainly welcome when the top challenge in K-12 education is narrowing the achievement gap between groups of students. But it's important to note that some of those gains — especially the increases in the last year — were helped along by changes in high school graduation requirements.

In 2012, Minnesota teens were required to pass Graduation Required Assessment for Diploma (GRAD) tests in reading and writing to graduate. However, last year the Legislature dropped the requirement.

That change alone boosted the rates, according to several school district representatives and advocates of GRAD. But state education leaders said they were encouraged by the data because students of color made significant gains year over year.

Education Commissioner Brenda Cassellius attributes the improvement to policies and investment in education carried out by Gov. Mark Dayton's administration and by the Legislature, as well as "the incredible work being done each and every day by Minnesota's educators."

Minnesota's grad rate increase is consistent with national trends. According to a 2013 report by Harvard University economists, during the first 70 years of the 20th century, U.S. teen graduation rates rose from about 6 percent to about 80 percent, and that consistent expansion of more educated workers pushed economic growth for decades. But between 1970 and the late 1990s, those rates stagnated, with overall numbers dipping below 75 percent — and much lower for lower-income students of color.

Yet in the early 2000s, the grad rates started climbing again. According to the National Center for Education Statistics, roughly 79 percent of high-schoolers now graduate within four years nationwide.

Harvard researcher Richard Murnane has said it's tricky to fully explain the ups and downs of high school graduation rates. He speculates that some high school students leave schools when graduation standards are raised.

It's also possible that the recent grad rate improvements could have been fueled by the additional focus placed on math and reading skills because of tests required under the No Child Left Behind federal rules. And the recession could have prompted more students to complete high school rather than hunt for jobs.

Without more research over a longer period, there's no clear answer to the question posed at the beginning of this editorial. While it's good to see more students graduating, it's imperative that their diplomas mean something. States and schools must not allow students to graduate if they have not mastered basic skills.

Minnesota state education leaders say they have improved not only graduation rates, but standards and academic rigor. They say a new strategy of testing to determine where students need academic help — then eventually using an ACT-type test toward the end of high school — will result in more students graduating and going on to college or some other postsecondary training.