Two Way Immersion is based on 3 important premises:
A second langauge is best acquired by language minority students when their first language is firmly established, and a second language is best developed by language majority children through immersion in that second language. Neither group is at risk of loosing their home language under these circumstances, thereby promoting additive bilingualism for both groups.
Knowledge learned through one language paves the way for knowledge aquisition in the second language. Students who learn content in one language are expected to demonstrate content knowledge in the second language once they acquire the language skills to express that knowledge.
Students need to reach a certain level of native language proficiency in order to facilitate second language development. Long-term cognitive advantages of bilingualism, will not accrue until the student has sufficiently developed both languages. This takes between 4 to 6 years.
Based on the work of Dr. Kathryn Lindholm, Associate Professor of Education at San José State University