Tyrone Pittman, dean of students at Simon Elementary School in Washington, crosses second-grader Moses Hamilton off his absentee list in April 2014. (Evelyn Hockstein/For The Washington Post)

Robert Balfanz is director of the Everyone Graduates Center at Johns Hopkins University. Leslie Cornfeld is special adviser to Education Secretary John B. King Jr.

Our nation’s education system is based on the notion that students are in school every day. That comforting assumption was shattered this week when the Education Department released the first national accounting of chronic student absenteeism. The data are staggering. Thirteen percent of all K-12 students — more than 6.5 million nationally — miss three weeks or more of school a year. Tragically, it’s worse in poor communities. There’s also a racial dimension: Among black and Latino students, the rate is 20 percent — 1 in 5.

The impact of this is devastating. Frequent absenteeism leads to poor academic achievement and dropping out. Missing so much school in the early years reduces the likelihood that students will read at grade level by third grade. From eighth to 12th grade, absenteeism is a better predictor than test scores of who will drop out. It’s also an entry point for the school-to-prison pipeline. In New York City, 79 percent of juveniles arrested were chronically absent from school before their arrest. Those who drop out are substantially more likely to be incarcerated and live in poverty.

Behind these statistics are countless kids who desperately want to do well. Circumstances beyond their control often drive absences: poor health, frequent moves, caring for relatives, working to help support families, bullying, gangs and dangerous routes to school. And some students don’t go simply because no one seems to care whether they show up.

The good news is that this is a problem we can do something about.

The Education Department’s data on chronic absenteeism provide rates by school, district and state, as well as by subpopulations, including race. The data, which will be released biannually in the future, will shine an important light on places where the problem is dire — and where interventions are most needed. Using chronic absenteeism as an early-warning sign will allow states, districts and schools to step in before it becomes easier to drop out than catch up.

But data alone will not reduce chronic absenteeism. We need to combine statistics with the human touch. To turn absences into attendance, we must form supportive relationships with chronically absent students and their families. We have seen this work in New York City, where combining weekly data reviews with school-based “success mentors” who responded to every absence and helped students and families address the root causes of absenteeism helped chronically absent students gain an educationally significant nine additional days of school. Effects were greatest for students living in poverty and in temporary shelter; high school students with mentors were 52 percent more likely to remain in school the following year.

Now, in what could be game-changing for efforts to close the achievement and graduation gaps, the White House, the Education Department, the Everyone Graduates Center at Johns Hopkins University and 30 communities across the nation are mobilizing a low-cost army of trained “success mentors” to reduce chronic absenteeism among the students most likely to fall off track. These are caring adults already connected to our schools — including school staff, security guards, coaches, after-school providers and AmeriCorps members.

This federal cross-agency effort, called Every Student, Every Day, is part of President Obama’s My Brother’s Keeper initiative, which aims to level the playing field for boys and young men of color and other young people. The project includes a national awareness campaign and, occurring this week, the first national action summit on chronic absenteeism, training hundreds of educators and other stakeholders. Our new education law, the Every Student Succeeds Act, also spotlights this metric to strengthen the quality and equity of all of our schools.

Reducing chronic absenteeism is not a fix for all educational challenges. But the many reforms underway in our nation’s schools can succeed only when the kids they are designed to help are actually there.