States' annual testing data for spring 2021 showed that unfinished learning in the wake of COVID-19 is most pronounced--and most troubling--in math. In Texas, nearly 40 percent of students failed the state's math exam in 2021. In Indiana, only 37 percent were proficient in math, down from 48 percent in 2019. Many states saw similar results. What makes the results such a cause for alarm is the sequential nature of math learning. Math skills build like a staircase. Should math teachers deliver grade-level content to students, knowing they lack the prerequisite skills and concepts to thrive? Or should she remediate by teaching the entire class fourth-grade material, which potentially robs students of the chance to outperform expectations? These questions plagued educators long before COVID-19. But given what test results say about unfinished learning, particularly in math, the need for answers is even more urgent.