Preliminary data from the DC Office of the State Superintendent on Education in February of 2016, seems to confirm the findings by longitudinal studies on achievement in dual language programs from across the United States.
DC Immersion believes it is time to prioritize the cross-sector research on achievement in the District’s dual language programs, so that the District’s future policies may be grounded in solid District-wide data.
George Mason University professors Thomas and Collier in their longitudinal research in North Carolina public schools found that students in dual language classrooms achieved significantly higher test scores regardless of race, socioeconomic status, special needs and language spoken at home. Interestingly, they also found increased attendance and fewer behavioral referrals in dual language classes.
The most recent rigorous longitudinal study conducted in Portland Oregon by Rand Corporation and American University finds much the same
Here is a collection of research on how Language Immersion affects cognitive development by ACTFL, the American Council on the Teaching of Foreign Languages.