SEATTLE - The finding was hard to believe, but year after year and in state after state, the numbers kept bearing it out: Sixth-graders who missed 20 days of class had, at best, a 20 percent chance of graduating from high school on time.
This was a bombshell for researcher Bob Balfanz, who'd spent most of his career trying to understand the factors driving 1 million American students to drop out each year. He'd paced school hallways and sat through hundreds of hours of classroom instruction.
But in 2007, after tracking 13,000 middle-schoolers for eight years in Philadelphia, Mr. Balfanz finally isolated a red flag common to all who, years later, failed to graduate on time: a history of poor attendance.
"You'd think, 'Hey it's only sixth grade, you can recover and grow out of this,' " he said.
Yet Mr. Balfanz, based at Johns Hopkins University in Baltimore, found that missing as few as 10 days a year has a cumulative impact, weakening the foundation upon which all other school achievement builds.
More surprising still, school attendance averages, while widely reported, are highly misleading. A district may accurately note rates of 90 percent, but still have hundreds of students missing weeks of instruction because that number is an aggregate - concealing the fact that different students are absent on different days.
"That's when the sheer magnitude hit us," said Mr. Balfanz, who recently released the findings of a major study on this effect.
Other researchers have found a similar relationship between poor attendance and low performance among rural kids, preschoolers and middle-class youth alike.
"Wherever we've looked, we've seen a clear relationship between missing a month of school and negative educational outcomes later," Mr. Balfanz said. "That has been proven for all kids."