Mathematical proof is a fundamental component of the undergraduate mathematics curriculum for mathematics majors. To teach students the deductive nature of mathematics and how to write proofs that meet an acceptable level of rigor and clarity, mathematics professors require students to write proofs for homework and tests. The professors then grade the proofs by writing marks and comments on them, assigning each proof a score, and returning the papers to the students. A larger study examined this process of grading students’ proofs, including the question of whether mathematics professors agree in their evaluation and scoring of students’ proofs. This poster focuses on one finding of the larger study, namely, that the scores assigned to the proofs by the professors varied considerably. Four reasons are discussed for the spread in the scores: (a) performance errors, (b) disposition toward grading, (c) judgments about the seriousness of errors and the student’s level of understanding, and (d) contextual factors.