As the coronavirus (COVID-19) pandemic closes schools across the nation, education systems are scrambling to meet the needs of schools, families, and 55.1 million students. The economic impacts and trauma of recent events will also have far reaching effects that will likely exacerbate long-standing opportunity gaps. While it is difficult to speculate on what missing months of school may mean for student achievement, research on seasonal learning and summer learning loss can offer some insights that can help educators, policy makers, and families understand, plan for, and address some potential impacts of this extended pause in classroom instruction when students return to school. To provide preliminary estimates of the potential impacts of the extended pause of academic instruction during the coronavirus crisis, the authors leverage research on summer loss and use a national sample of over five million students in grades 3-8 who took the Measure of Academic Progress (MAP) Growth™ assessments in 2017-2018. They examined how the observed typical average growth trajectory by grade for students who completed a standard-length school year compares to projections under two scenarios for the closures: a COVID-19 slide, in which students showed patterns of academic setbacks typical of summers throughout an extended closure and COVID-19 slowdown, in which students maintained the same level of academic achievement they had when schools were closed (modeled for simplicity as March 15, with school resuming in fall).