Substitute teachers are an important (yet oft-ignored) group of educators in the U.S. school system. The reason is simple: Substitute teachers spend substantial time with K-12 students. Like other professionals, teachers are absent from work for various reasons, such as sickness, professional development, or personal issues. Based on one estimate drawn from a sample of large U.S. metropolitan districts, teachers miss an average of about 11 days out of a 186-day school year. This means that students spend, on average, approximately two-thirds of a school year with substitute teachers during the entirety of their K-12 schooling—not a trivial amount of time.
Teacher absences are not only common, but also detrimental to student learning. Based on one study, 10 additional teacher absences lead to 1.2% and 0.6% of a standard deviation decrease in math and English Language Arts test scores, respectively. Several other research papers using data from multiple contexts reached similar findings. Higher-quality substitute teachers may be able to mitigate some of the negative impacts of teacher absences. Indeed, one study shows that certified substitute teachers are more effective than their uncertified peers.
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