Every year 1.2 million students fail to graduate from high school – equivalent to a drop out rate of over 7 thousand students per school day. A more detailed investigation of that number reveals that Culturally and Linguistically Diverse (CLD) students are significantly overrepresented in that group. Yet, high school CLD students have received little attention from educational researchers over the past decades. This is even more alarming since all recent demographic studies point to an increase of the CLD population in the years to come. This book, therefore, starts to shed some light on this topic by: (i) compiling and integrating all the relevant existing literature on second language acquisition; (ii) discussing the challenges faced by high school CLD students and explaining why current instructional practices are not meeting their needs; and (iii) pointing to an alternative approach that better addresses high school CLD students'' needs. This book should become a much needed reference for both teachers and administrators, providing invaluable insights that should ultimately help improve the education offered to high school CLD students.