This study leverages natural language processing to assess dimensions of language and discourse in students’ discussion board posts and comments within an online learning platform, Math Nation. This study focusses on 1,035 students whose aggregated posts included more than 100 words. Students’ wall post discourse was assessed using two linguistic tools, Coh-Metrix and SEANCE, which report linguistic indices related to language sophistication, cohesion, and sentiment. A linear model including prior math scores (ie, Mathematics Florida Standards Assessments), grade level, semantic overlap (ie, LSA givenness), incidence of pronouns, and noun hypernymy accounted for 64.48% of the variance for the Algebra I end of course scores (RMSE= 13.73). Students with stronger course outcomes used more sophisticated language, across a wider range of topics, and with less personalized language. Overall, this study confirms the contributions of language and communication skills over and above prior math abilities to performance in mathematics courses such as Algebra.