Background or Context: Dual language education aims to foster the development of bilingualism, biliteracy, sociocultural competence, and academic skills in all school subjects. Early correlational research suggests that participation in dual language education is associated with higher achievement. Recent studies leveraged more comprehensive sets of baseline characteristics and found that dual language students improved their achievement status more than other students. A major limitation to these studies is their lack of ability to model within-student growth. Thus, we lack evidence on the relationship between dual language education and growth trajectories within and across grades. Purpose: This paper reports academic achievement and growth in grades 2 through 8 for Hispanic participants and nonparticipants of a Spanish--English dual language program. It extends the literature by providing novel evidence on seasonal patterns of learning for multilingual students across the elementary and middle grades. Research Design: Applying a piecewise multilevel model to rich assessment data on a large sample of Hispanic students in a district in the Midwest, I compare the math and English reading growth rates of participants to nonparticipants of a dual language (DL) program. By separately specifying growth terms for each school year and summer, I test whether any differences in growth rates between DL and non-DL students expand, stay the same, or diminish across grade levels. Conclusion: Dual language participants started second grade with lower achievement than nonparticipants. In math, dual language participants grew more than nonparticipants during each year in grades 2 to 5 but lost more learning during summers. In English reading, dual language participants grew more during some school years. These findings suggest summer learning opportunities are crucial for addressing achievement disparities.