Student enrollment and transfer patterns between the traditional public and charter school sectors help shape the role of charter schools in the broader educational ecosystem, especially as related to the enrollment and segregation of low-income students, English learners, students of color, and students in special education. We examine patterns of student transfer between traditional public schools and charter schools among four of Texas's largest charter networks, which cumulatively make up over one-third of Texas charter students. We find that these schools serve fewer special education students than traditional public schools, but a greater share of low-income and English learners. Transfers between sectors contribute to enrollment gaps in special education and other classifications, but the findings do not apply uniformly across charter districts, student enrollment classifications, or grade levels. These findings highlight nuanced enrollment patterns between the charter sector and traditional public schools, suggesting that differences in student characteristics between sectors likely stem from a range of sources. Policymakers should acknowledge this nuance, consider alternatives to blanket enrollment regulation policies, and conduct similar analyses of enrollment patterns among charter districts.