The two-way immersion program Filière Bilingue (FiBi) is a choice-based educational alternative in a public school in Biel/Bienne. It integrates French-speaking, German-speaking and allophone students and strives to promote bilingualism and biliteracy in addition to grade-level academic achievement. This book presents a longitudinal study of oral proficiency development of K-4 learners in French and German (languages of schooling). Data were collected over four years and analyzed by using a mixed-method approach. Whereas the quantitative analysis shows the emergent multilinguals' ability to use the two languages communicatively, the qualitative analysis provides some illustrative translanguaging examples of learners in their beginning stages of moving along a bilingual continuum.