Worker absence is a frequent phenomenon but little is known on its effects on productivity nor on organisations' strategies to cope with this temporary disruptive event through substitute workers. Using a unique French administrative dataset that matched missing secondary school teachers to a substitute teacher, Dr Asma Benhenda finds that the expected loss in daily productivity from teacher absences is on par with replacing an average teacher with one at the 15th percentile of the teacher value-added distribution. On average, tenured substitute teachers are able to compensate 37% of this negative impact while contract substitute teachers do not have any statistically significant impact. This result has important implication for public policy in the context of the shortage of tenured teachers in disadvantaged areas, where contract teachers are more and more concentrated.