The "Next Generation Science Standards" ("NGSS") call for a high level of classroom discourse (Lee, Quinn, and Valdés 2013). To engage all students, including English learners (ELs), in this form of discourse, educators have turned to talk moves (e.g., "Say more about that"), defined as general-purpose tools for facilitating academically productive discussions (MacDonald, Cook, and Miller 2014). However, the generic nature of talk moves may limit their utility in guiding students' sense-making and promoting science understanding. In this article, the authors propose the notion of discipline-specific probes, which go beyond general-purpose talk moves by targeting specific science concepts and ideas. Next, they present a heuristic developed by their research team in collaboration with a teacher advisory board for generating discipline-specific probes to facilitate discussions around scientific models. Third, they follow one teacher back into her fifth-grade classroom to see how she uses the heuristic to guide students' sense-making and promote science understanding. Lastly, they provide recommendations for teachers to implement the heuristic in their classrooms.