We investigate student mobility in a choice-based system that has gone to scale, New Orleans, to gain insight into an underlying improvement mechanism of choice-based reform and its potential equity-related consequences. In contrast to typical analyses of mobility, this study distinguishes incumbent school characteristics that can cause students to search for a new school ("push" factors) from those features that can draw families to a new school ("pull" factors). We find evidence consistent with school performance playing both push and pull roles. However, for low-achieving students, the push of low performance at incumbent schools is stronger than the pull of high performance at potential destinations, implying that low-achieving students are more successful in exiting low-performing schools than they are in finding higher-performing schools to attend.