Given recent questions regarding the construct validity of Cahn and Shulman's Feelings of Understanding/Misunderstanding scale, two studies were conducted to develop a low-inference, behavioral measure of students' perceived understanding in the college classroom. In Study One (N = 265), a pilot inventory was developed to measure students' perceptions of instructor behaviors that communicate understanding and/or misunderstanding in the college classroom. In Study Two (N = 261), confirmatory factor analyses supported the hypothesized item loadings from the pilot inventory and yielded a new, Student Perceptions of Instructor Understanding Scale (SPIUS). Correlation analyses revealed meaningful associations between the new measure and students' perceptions of teacher confirmation, verbal aggressiveness, and credibility. (Contains 2 notes and 3 tables.)