This study examines the effects of internal migration driven by severe natural disasters on students in host communities, and the mechanisms behind these effects, using the large influx of migrant students into Florida public schools in the aftermath of Hurricane Maria. I find significant adverse effects of the influx in the first year on existing student test scores, disciplinary problems, and student mobility that vanish entirely in the second year. These adverse effects are particularly pronounced among higher-performing students who were proficient on prior year tests: A 5-percentage point increase in migrant share at the school-cohort level decreases test scores of these students by 0.09 standard deviations in math (0.07σ in ELA), increases disciplinary incidents by 50 percent, and student mobility by 44 percent in the first year. I also find evidence that compensatory resource allocation within schools is an important factor driving the adverse effects. In particular, the results provide evidence that schools reallocate resources – teachers in particular – in a compensatory fashion when faced with a large influx of high-need students, increasing the likelihood that higher-performing students are assigned to less effective teachers.