BUFFALO, N.Y. (AP) — A new report finds that about 16 percent of teachers in some of the country’s largest public school districts are considered chronically absent and out of the classroom 18 days or more for illness, personal time or professional training.

But the findings from the National Council on Teacher Quality say that even teachers in line with the average of 11 days out may be hurting students’ progress.

The Washington-based group’s look at 40 districts found that, on average, teachers were present 94 percent of the 2012-13 school year, missing nearly 11 days.

Seventy-one percent of absences were for illness or personal leave, with the rest school business.

The National Education Association says districts are looking for ways to give teachers necessary time out to collaborate and improve while discouraging illegitimate absences.

The report also found no relationship between teacher absence and the poverty levels of a school’s students, nor any difference in absentee rates among districts with policies meant to encourage attendance, such as paying teachers for unused sick time, and districts without those incentives.