The Undergraduate Knowledge of the Mathematics Graduate School Application Process (Knowledge-GAP) project seeks to understand how undergraduate student knowledge about the graduate school application and admissions processes acts as a barrier for students seeking advanced degrees in mathematics. The project is especially interested in experiences of students historically marginalized in STEM disciplines as they attempt to pursue graduate education in mathematics. This presentation on preliminary data from this NSF funded project (Award # 2126018) will discuss how access to mentors have impacted participants' ability to apply to graduate school.