Mid-adolescence has been identified as a period of considerable potential growth in the language skills and practices that support reading and writing at school, but little research has examined mid-adolescents' use of connectives in school-relevant persuasive writing. In this study, we define connectives as cohesive devices that signal to a reader logical relations between ideas or organizational relations in a text. Drawing from Halliday and Matthiesen (Halliday's introduction to functional grammar, Routledge, 2014) and Hyland (Metadiscourse: exploring interaction in writing, Continuum, 2005), we propose a comprehensive taxonomy of connectives that guided our examination of developmental trends and individual differences in the use of connectives in persuasive essays written by a socioeconomically and ethnically diverse cross-sectional sample of U.S. public-school mid-adolescents in grades 5 to 8 (N = 512). Our analysis revealed (1) developmental trends and individual differences at different grade levels and (2) identified students' connective use as a predictor of overall writing quality above and beyond students' receptive language skills and sociodemographic factors.