Providing opportunities for students to talk directly with their peers is a critical dimension to facilitating discussions in mathematics and science, including argumentation-focused discussions in which students construct arguments and critique others' arguments. Research suggests that supporting student-to-student talk and facilitating argumentation discussions are complex and challenging practices for preservice teachers (PSTs). Elementary PSTs from two mathematics and two science methods courses practiced facilitating student-to-student talk within the context of an argumentation-focused discussion. This study's main purpose was to explore the prompts that 29 PSTs used to encourage student-to-student talk in a simulated classroom. Findings show the PSTs were able to use direct prompts that encourage student-to-student talk but were just as likely to use prompts that may discourage students from talking to each other. Most direct prompts PSTs used to encourage student-to-student talk were for the purpose of argumentation construction and/or critique. PSTs were more likely to use indirect prompts, much like Talk Moves, that encourage students to consider others' ideas rather than requesting that students talk with each other. These findings have important implications for future research, as well as for teacher educators and professional learning facilitators who support teachers learning to encourage student-to-student talk during argumentation-focused discussions.