Prevalent characteristics of effective mathematical discourse in the literature include student autonomy, a positive social environment, and a degree of perceived mathematical competence. These characteristics are also found in Self-Determination Theory (SDT), which posits that actions are self-regulated when students' autonomy, competence, and social relatedness are fulfilled. Utilizing SDT as an additional lens for examining student engagement in whole class discussions, this study examined high school students' observed discourse actions and mathematical talk in the context of their self-reported psychological needs of autonomy, competence and relatedness. Results suggest that students' perceived needs correspond with their engagement in making mathematical statements in the context of classroom mathematical discussions. However, students who lack in one or more need can be supported by participation of peers with more fulfilled needs.