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Teacher-written postcards to reduce absences
Last registered on July 13, 2020


Trial Information
General Information
Teacher-written postcards to reduce absences
Initial registration date
July 10, 2020
Last updated
July 13, 2020 3:46 PM EDT
Primary Investigator
Center for Education Policy Research at Harvard University
Other Primary Investigator(s)
PI Affiliation
Dartmouth College
Additional Trial Information
Start date
End date
Secondary IDs
A randomized field experiment in which parents of early elementary students received personalized information about the academic content their child missed when absent. Following an absence, school staff sent postcards to parents detailing how many days of school their child had missed alongside a handwritten note from their teacher summarizing the academic material covered during the absence. We randomized the intervention across schools and classrooms in two urban school districts. The sample consisted of over 5,500 students in preschool through second grade. Overall, the treatment reduced absences.
External Link(s)
Registration Citation
Kane, Tom and Douglas Staiger. 2020. "Teacher-written postcards to reduce absences." AEA RCT Registry. July 13. https://doi.org/10.1257/rct.6013-1.0.
Sponsors & Partners

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Experimental Details
The intervention consisted of sending postcards home to reduce student absences in early grades (pre-kindergarten to grade 2). Following each absence, parents received a postcard from their child’s teacher indicating the number of days their child had missed that school year and describing the academic content covered during their recent absence. Though broadly similar, the two districts implementing the intervention differed in delivery method and some of the content and visual design of the postcards. In one district, the postcards showed students’ cumulative absence counts on a scale from one to nine, with a note that the student is “missing a lot of learning” at the peak of the scale. Teachers provided students with the postcard on their first day back following an absence, with instructions to bring it home to their parents. The other district had a slightly different postcards design. The scale for its Fall postcard ends at “4+” absences with a note reading, “Urgent--- Call us!”; the upper-limit of the scale increased by four absences each quarter. In this district, central office workers mailed the postcards on Fridays for all absences that occurred during the school week.
Intervention Start Date
Intervention End Date
Primary Outcomes
Primary Outcomes (end points)
Student days absent
Primary Outcomes (explanation)
Count of the number of days a student was absent during the follow-up period.
Secondary Outcomes
Secondary Outcomes (end points)
Secondary Outcomes (explanation)
Experimental Design
Experimental Design
Randomized control trial with two school districts. In one district, schools were randomly assigned with equal allocation to either control or treatment groups, blocking on levels of the schools’ average absence rates in the prior year. We constructed the blocks by evenly dividing schools into three groups based on their average absence rate and then randomly assigned half the schools in each block to treatment and the other half to control. In the second district, classrooms in grades Pre-K to 2 were randomly assigned to treatment or control blocking on school and grade level. Units were allocated to the control and treatment groups with equal probability.
Experimental Design Details
Randomization Method
Randomization was done using a Stata program.
Randomization Unit
School level randomization for one school district and classroom level randomization for the other district
Was the treatment clustered?
Experiment Characteristics
Sample size: planned number of clusters
18 schools and 107 classrooms
Sample size: planned number of observations
5874 students
Sample size (or number of clusters) by treatment arms
9 schools and 53 classrooms for control (2553 students) and 9 schools and 54 classrooms for treatment (2999 students)
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
Supporting Documents and Materials

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IRB Name
Harvard University Area Institutional Review Board
IRB Approval Date
IRB Approval Number
Post Trial Information
Study Withdrawal
Is the intervention completed?
Intervention Completion Date
June 25, 2019, 12:00 AM +00:00
Is data collection complete?
Data Collection Completion Date
August 01, 2019, 12:00 AM +00:00
Final Sample Size: Number of Clusters (Unit of Randomization)
9 schools and 53 classrooms (control) and 9 schools and 54 classrooms (treatment). 125 clusters in total.
Was attrition correlated with treatment status?
Final Sample Size: Total Number of Observations
5552 students
Final Sample Size (or Number of Clusters) by Treatment Arms
2553 students control and 2999 students in treatment
Data Publication
Data Publication
Is public data available?
Program Files
Program Files
Reports, Papers & Other Materials
Relevant Paper(s)