Despite
the fact that the average American student is absent more than two weeks out of
every school year, most research on the effect of instructional time has
focused not on attendance but on the length of the school day or year. Student and school fixed effects models
using Massachusetts data show a strong relationship between student absences
and achievement but no impact of lost instructional time due to school
closures.
This study confirms those findings
in instrumental variables models by exploiting the fact that moderate snowfall
induces student absences while extreme snowfall induces school closures. Prior work ignoring this non-linearity
may have mis-attributed the effect of absences to such snow days.
Each absence induced by bad weather
reduces math achievement by 0.05 standard deviations, suggesting that
attendance can account for up to one-fourth of the achievement gap by
income.
That absences matter but
closures do not is consistent with a model of instruction in which coordination
of students is the central challenge, as in Lazear (2001). Teachers appear to deal well with
coordinated disruptions of instructional time like snow days but deal poorly
with disruptions like absences that affect different students at different
times.
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