Student mobility is defined as students transferring, or changing, schools during the school year (within-year mobility) or summer (between-year mobility) and is pervasive in many large, urban school districts, including Philadelphia. In the School District of Philadelphia (SDP), rates of student mobility are high: one-third of high school students either experienced mobility or dropped out of school from SY2013-14 through SY2016-17. Student mobility can be challenging for both students and schools, and school districts, including in Philadelphia, have worked to reduce mobility and mitigate its negative impacts. Research suggests that some student groups--including students who are English Learners--are more likely to experience mobility, an equity concern given the negative association with educational outcomes. It is crucial to recognize that English Learner students are a diverse group, and more attention should be paid to the important variation within this group regarding how they experience mobility. To further the understanding of how EL students experience mobility in SDP, this study explores the mobility rates among students with a more nuanced approach that explores variation in experiences among EL students. This study addresses two research questions: (1) What are some of the reasons students transfer schools, particularly ELs? and (2) How does within- and between-year mobility vary by EL status and length of EL classification?