Reformed science curricula provide opportunities for students to engage with authentic science practices. However, teacher implementation of such curricula requires teachers to consider their role in the classroom, including realigning instructional decisions with the epistemic aims of science. Guiding newcomers in science can take place in settings ranging from the classroom to the undergraduate research laboratory. We suggest thinking about the potential intersections of guiding students across these contexts is important. We describe the Classroom-Research-Mentoring (CRM) Framework as a novel lens for examining science practice-based instruction. We present a comparative case study of two teachers as they instruct undergraduate students in a model-based inquiry laboratory. We analyzed stimulated-recall episodes uncovering how these teachers interacted with their students and the rationale behind their instructional choices. Through the application of the CRM Framework, we revealed ways teachers can have instructional goals that align with those of a research mentor. For example, our teachers had the goals of "creating an inclusive environment open to student ideas," "acknowledging students as scientists," and "focusing students on skills and ideas needed to solve biological problems." We suggest three functions of research mentoring that translate across the classroom and research laboratory settings: (1) build a shared understanding of epistemic aims, (2) support learners in the productive use of science practices, and (3) motivate learner engagement in science practices.