About one in six teachers in some of the country's largest public school districts are out of the classroom at least 18 days, or more than 10 percent of the time, for illness, personal reasons and professional development, according to a report out Tuesday that urges districts to make teacher attendance a higher priority.
Even teachers in line with the average of 11 days out may be hurting their students' progress, the National Council on Teacher Quality said.
"Given the time and attention spent on school programs, new curriculum and strategies to strengthen teacher quality," the report's authors wrote, "we may be overlooking one of the most basic, solvable and cost effective reasons why schools may fail to make education progress."
The Washington-based think tank examined data provided by 40 large school districts for the 2012-13 school year and found that, on average, teachers were in the classroom 94 percent of the 186-day school year. About 71 percent of the time taken was because of illness or personal leave, with the rest for school business.
The American Federation of Teachers' president, Randi Weingarten, said "an overall 94 percent attendance rate shows the extraordinary dedication of teachers across the country."
The report cited studies showing students suffer when teachers are out 10 days.
"Yet in the average classroom in this study, teachers exceed this level of absence, often for perfectly legitimate reasons and even in pursuit of becoming a more effective instructor," it said.
About 16 percent of teachers missed 18 or more days and were considered chronically absent, accounting for almost a third of all absences. The same percentage missed 3 days or less.
The National Education Association said the report alone would not change the way school districts approach attendance but that the single-year snapshot fit with larger discussions about why teachers miss school and how to give them time out to collaborate and improve.
Some districts have raised standards for substitute teachers to accommodate for such "productive absences," said Segun Eubanks, director of teacher quality for the National Education Association union, but others still require only a high school diploma.
To train teachers only while students are off is prohibitively expensive at more than $2 million a day for a large district, he said.
The NCTQ report found districts spend an average of $1,800 per teacher to cover absences each year.
New Hampshire social studies teacher Ben Adams said it's rare he's anywhere but his classroom when school is in session because his consistent presence is part of the learning environment he cultivates.
"Attendance for a teacher, it's not curriculum, it's not the star of the show, but it's one of those subtle things that goes a long way to dealing with other parts of teaching -- classroom management, trust, risk," the Salem High School teacher said.
Omaha, Nebraska, teacher Maddie Fennell, on the other hand, said her national work around professional development and policy took her out of the classroom 20 to 30 days some years and her students and the others in her building have benefited by posting measurable academic gains.
"When I go out and do this work, I come back and bring the learning with me back to my school," she said, adding that a consistent substitute teacher has helped.
Among the report's other findings, while some districts, including Indianapolis and the District of Columbia, had both higher rates of teachers with excellent attendance -- three or fewer days absent -- and lower rates of chronically absent teachers, that wasn't the rule.
Buffalo Public Schools, for example, had the second-highest rate of excellent attendance (30 percent) of the 40 districts studied but also the highest rate of chronically absent teachers (37 percent) in 2012-13. The district did not respond to requests for comment.
The report also found no measurable 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.