Everyone knows that student achievement often suffers when children and families move, leaving behind their school and neighborhood, yet, in urban districts like Los Angeles, mobility is now encouraged by the development of mixed-markets of diverse schools, including charter, pilot, and magnet schools in. Over 60 new school facilities were opened as well during 2002-2008 period, thanks to a $27 billion construction program undertaken by the Los Angeles Unified School District (LAUSD). In this paper, the authors first assess how student attributes and differing school organizations, varying by type and quality, influence the rates of student exit prior the end their school's grade cycle within elementary and secondary schools. They estimate the discrete influence of student factors and school types on the likelihood that pupils leave their school, using what are known as hazard-rate models, based on 4.5 million person-period observations. They find contrasting patterns of student mobility along ethnic lines: African American and White students were more likely to exit their school, compared with Latino, non-English speaking, and foreign-born students, yet students attending overcrowded schools--disproportionately situated in low-income Latino neighborhoods--exited at higher rates. Charter and magnet school students left their schools at much lower rates, compared with peers in regular schools, after taking into account prior effects of family background. The opening of new high schools slowed student mobility substantially. Furthermore, they discuss implications for conceptualizing student mobility--especially the capacity of charter and magnet schools to slow student mobility--as diverse portfolios of schools come to characterize urban areas like Los Angeles. Various grade structures for LAUSD schools are appended. (Contains 4 figures, 7 tables and 11 endnotes.)