Minnesota high schools reached a milestone last year: Nearly 83 percent of students got their diplomas on time — a record high graduation rate. According to the state Department of Education, that's an improvement of just over 4 percentage points from 2012 to 2017.

For the same period, the number of graduates taking remedial, catch-up courses during their first two years at state colleges and universities dropped by 26 percent, suggesting that more Minnesota students are leaving high school prepared.

Those trend lines are slowly moving in the right direction, but too many state kids are still too far behind. Other measures show that even as more Minnesota teens finish K-12, unacceptably high numbers of them are not mastering the basics. Statewide test scores have remained flat in recent years, and the stubborn achievement gap between white students and those of color persists.

As former Minneapolis Public Schools Superintendent Peter Hutchinson argued in a Star Tribune commentary, the National Assessment of Educational Progress assessments, given every four years to a sample of state students, have shown no significant improvement in the past decade. Only 40 to 50 percent of Minnesota students taking those tests were considered proficient in both reading and math. And though Minnesota regularly has among the highest ACT college entrance exam scores among the states, only 30 percent of students taking the exam here meet all of the ACT's benchmarks for college readiness.

The graduation data showed varying levels of improvement for all groups and some districts where disparities have narrowed. Still, a difference of almost 19 percentage points remains between the two groups. More that 88 percent of whites graduated, compared with about half of American Indian students and about two-thirds of black and Latino students.

State Education Commissioner Brenda Cassellius and Superintendents Joe Gothard in St. Paul and Ed Graff in Minneapolis were pleased with the limited progress, but acknowledged the pressing need to do more to improve academic achievement for more students.

"While we recognize these accomplishments, we must be sure [Minneapolis Public Schools] graduates leave school fully prepared for college and career," Graff said in a statement. "We know what we're doing right — but what can we do now to see the same gains in achievement that we're seeing in graduation?"

To address that question, the Minneapolis district is focusing on literacy, expanding student support systems and increasing credit-recovery opportunities. In St. Paul, the district recently announced a plan for improving literacy and math skills as well as kindergarten readiness. And Cassellius says her department will send support to high schools with low graduation rates to address school-specific needs.

Those are worthy initiatives, but they'll require sticking with instructional models that work and letting ineffective programs go. It will take focused instruction and support from families and communities. The state has set a goal to have a 90 percent graduation rate statewide by 2020, with no student group falling below 85 percent. With students of color still below 70 percent, that target will not be met given the current rate of improvement.

Steps musts be taken to speed up the use of strategies that work for struggling learners. Unless that happens, higher graduation rates won't necessarily translate into well-educated students.