Academic language is a kind of social language for the purpose of schooling. It is central to disciplinary learning, thinking, and communication. This study examined adolescents' use of academic language in informational writing, a genre highly valued in school, workplace, and society. Ninety-three seventh and ninth grade students from a U.S. public school were asked to write a science report based on a "wordless" picture book about a familiar class of animals called crocodylia. The student writing corpus was coded for presence of a constellation of academic language features. Statistical analyses of these data showed that (a) the adolescents made limited use of academic language features in their writing, (b) there were no significant differences between the two grade levels in academic language use, (c) there was a significant relationship between reading ability and academic language use, and (d) academic language use was a significant predictor of writing quality. These findings highlight both the importance of and the need for more explicit attention to academic language in secondary literacy instruction.