A Single Postcard Cut Chronic Absenteeism. A Six-District Follow-Up Found the Sentence That Mattered.
A 2017 randomized trial in Philadelphia found that one mailed postcard reduced student absences by about 2.4%. A 2025 replication across six districts found a smaller average effect overall, and a much larger one for messages that named a child's exact missed-day count.
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The postcard cost less than a dollar to print and mail. It said almost nothing: that attendance mattered, and, for half of the families who got one, exactly how many days that specific child had already missed. No phone call, no app, no follow-up. In a 2017 randomized trial run by the School District of Philadelphia with the Regional Educational Laboratory Mid-Atlantic, researchers Todd Rogers, Teresa Duncan, and four co-authors mailed that postcard to a randomly chosen half of families, and the postcard group’s kids missed about 2.4% fewer days of school over the rest of the year than the group that got nothing.
Two-point-four percent doesn’t sound like much until you multiply it across a district. Philadelphia enrolls roughly 200,000 students. A 2.4% reduction in absences applied district-wide is the rough equivalent of thousands of additional student-days in classrooms, from a piece of mail that costs less than a dollar to produce and send, cheaper than the sleep-schedule repair work most families are already doing this time of year to get a kid’s bedtime back under control before the first bell.
The result got picked up widely as a tidy case for behavioral nudges in education: cheap intervention, real effect, ship it. What took eight years to arrive was the harder question: does it generalize, and if so, why?
The follow-up that complicated the story
That question got a real answer in 2025, when Jonah Berger, James Bolyard, David Hersh, Lisa Sanbonmatsu, Douglas Staiger, and Thomas Kane published a six-district replication in the Journal of Research on Educational Effectiveness, testing several versions of the same idea across urban and suburban districts nationwide. The headline number was smaller than Philadelphia’s: about a 1.9% average reduction in absences, roughly 0.19 fewer missed days per student.
But the study didn’t stop at the average. It tested multiple versions of the message against each other, and the versions that named an exact, personalized count of missed days — not a generic reminder that attendance matters — reduced chronic absenteeism by 10% or more in some districts. The paper’s explanation is that most parents are carrying around the wrong number. They know their kid has missed “some” school. They don’t know it’s been eleven days. A message that states the real count corrects a factual error rather than a general attitude, and a corrected fact tends to stick longer than a mood does.
Parents managing their own mornings while also managing a kid’s attendance streak sometimes end up needing their own accountability system, not just their kid’s, which is a separate problem from the one this postcard solves and outside what either study measured.
Why the format probably isn’t the point
The two studies actually diverge somewhere more interesting than either headline number suggests. The original 2017 trial tested a generic version against a personalized-count version and found no statistically significant difference between them: both moved the needle by roughly the same amount, and Rogers and Duncan’s team said so plainly. The 2025 six-district replication is where the personalized version pulled ahead, sometimes by a lot, reducing chronic absenteeism by 10% or more against a generic reminder that barely moved anything. Read the two side by side and the conclusion isn’t “personalization always wins.” It’s that a single trial can miss a real difference a larger, more varied replication later confirms, which is a reason to trust the six-district number over the 2017 one wherever they disagree.
The 2025 paper’s own account of why personalization won this time: most parents underestimate how many days their kid has missed. “Please make sure your child attends school regularly” tells a parent nothing they didn’t already believe. “Your child has missed 11 of the last 60 school days” tells most parents something they didn’t know. That’s a narrower finding than the debate over whether counting infractions at all changes behavior in a workplace, where the number usually exists to justify discipline rather than to correct anyone’s mistaken belief about their own record.
Most districts already have the infrastructure to send a templated reminder every month; far fewer have bothered to pull the one number that would make it work, which is the actual count for that one kid. The research suggests that pulling the real number is most of the value, and it’s also the cheaper half of the problem to fix — cheaper than redesigning the message, cheaper than adding an app, cheaper than anything requiring a new vendor contract.
The part the mail can’t reach
Both studies measure days present. Neither measures why a family’s morning was hard on the days a kid was actually missed: a broken alarm routine, a single-parent household with no backup, a teenager who’s stopped listening to that particular parent. The postcard changes what a parent knows. It doesn’t touch what happens at 6:45 a.m. Those are two different problems, and so far only one of them has a randomized trial behind the fix. The other is closer to what most of the accountability research on this site actually covers: changing what happens at the moment the alarm goes off, a problem with its own body of evidence that has nothing to do with postcards.
It’s also a narrower fix than it can sound like in summary. A parallel dispute in the broader nudge literature is a useful check on how much weight any single percentage like 2.4% or 1.9% should carry on its own, postcard studies included.
FAQ
Does sending parents a postcard actually reduce school absences? Yes, by about 2.4% in the original 2017 Philadelphia trial, and by a smaller 1.9% on average in a 2025 six-district replication — though the personalized-count versions of that later study reduced chronic absenteeism by 10% or more.
Why does a postcard work better than a phone call or an app notification? The 2025 replication traced the effect to the information, not the paper format. Most parents underestimate how many days their child has missed; a message naming the real count corrects that belief, whatever the delivery channel.
Does this work the same for younger kids and teenagers? The original Philadelphia trial found no significant difference between grades 1–8 and grades 9–12. Correcting a parent’s belief about the actual count doesn’t obviously depend on the child’s age.