Little is known about the integration of social-emotional learning (SEL) with science instruction. We used a sequential mixed-methods design to examine (1) how fourth graders use argumentation practices and social gestures in science class and (2) how argumentation practices and social gestures differ between intervention and comparison classrooms. Intervention classrooms implemented Connect Science. Fourteen student conversations in seven classrooms were coded for argumentation practices (i.e., claims, evidence, and questions) and social gestures (i.e., agreement, disagreement, assertive speech, and prosocial speech). Across all classrooms, science conversations were most productive when students used social gestures to support use of argumentation practices. Without social gestures, conversations were disconnected or highly assertive. Proportionally, Connect Science students discussed science content more and discussed logistics less than comparison students. Findings include recommendations for conditions (i.e., SEL instruction, science reference materials, and time) to enhance scientific discourse and argumentation in elementary school classrooms.