Using a mixed methods comparative case study, the researcher explored the dual language contexts at each school before examining the second- through fifth-grade Spanish and English reading biliteracy trajectories. While both campuses' students experienced positive trajectories toward biliteracy by the end of fifth grade, each campus was characterized by different rates of biliteracy development, correlations between Spanish and English reading levels, and percentage of students in the biliteracy zone at each grade. The split plot MANOVA revealed that only school of attendance and initial English oral language levels explained the variance in biliteracy trajectories for students at these campuses. Taken together, these results provide needed nuance on contemporary biliteracy theory, especially as it relates to differing emergent bilingual subgroups within dual language programs.