High schools in Auckland, New Zealand and Adelaide, Australia, must respond to increasing social change. Auckland, identified as a “Super-diverse city,” has rapidly growing populations of Asian and Pasifika migrants and a large population of indigenous Māori. Adelaide is home to multiple generations of migrant families and growing numbers of newly arrived migrants and international students. High schools in both cities are microcosms of this expanding cultural and linguistic diversity. This chapter examines such schools, where students’ plurilingual practices are shaped by complex academic, social and personal demands. Focus is given to teaching strategies that support plurilingualism in English-dominant institutions.