Effects of Instructional Time: School Year v. School Day


To improve students’ academic achievement, some policymakers have called for increasing the amount of time students spend receiving instruction in school. Educational leaders thus frequently consider either extending the length of the school year or extending the school day. Derek Wu, from the Harris School of Public Policy at the University of Chicago, examined the effects of instructional time on academic achievement.

The Study: 

With nearly 900,000 student observations from eighty countries, this study utilized the Trends in International Mathematics and Science Study (TIMSS) Assessments data to examine the effects of changes in instructional time on 8th grade student achievement. The analysis disaggregated yearly instructional time into days per year and hours per day to assess the impacts of different instructional time measures on student achievement.

  • Overall, the author finds that positive student achievement effects are largely driven by the length of the school day, not the school year. Despite this, there are diminishing marginal returns to lengthening the school day.
  • Socioeconomically underprivileged students have larger gains from a longer school day, in comparison to their more socioeconomically privileged counterparts.
  • Increasing instructional time for non-tested subjects yields positive effects on test scores. This is especially pronounced for socioeconomically underprivileged students.
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