It's one of the oldest issues in school improvement: Getting kids to show up. If students miss 10 percent of the school year — that's just two days a month --research shows they are way more likely to fall behind — even drop out.

Today, the U.S. Education Department is releasing a report on the first national data set on chronic absence — defined as missing 15 or more days of school a year. The numbers come from the 2013-2014 Civil Rights Data Collection survey — an on-the-ground look from 95,000 schools.

The numbers are striking: More than 6 million kids are missing 15 days or more of school a year.

Chronic absenteeism rates are highest in high school: more than 2 million high schoolers are missing 15 days or more.

The figures for minority students are even more alarming: More than a fifth of black high schoolers are chronically absent. It's 20 percent for Latino high school students and 27 percent for American Indians and Native Alaskans.

"Even the best teachers can't be successful with students who aren't in class," said Education Secretary John B. King Jr. He warned that these numbers are alarming, especially in terms of the administration's efforts to focus on the persistent achievement gap between minority and white students.

This is a new metric for schools — many have not regularly collected information on chronic absenteeism. They, instead, used figures for average daily attendance — how many students show up on a specific day. Or they report figures for truancy — a more narrow number of unexcused absences that varies by state.

Experts argue that tracking absences by kid is a more useful data point.

Under the new federal education law, however, school districts will need to gather this information and report it — in order to be in compliance with the law.

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