Implicit Grading Bias In Large Language Models: How Writing Style Affects Automated Assessment Across Math, Programming, And Essay Tasks

Abstract

As large language models (LLMs) are increasingly deployed as automated graders in educational settings, concerns about fairness and bias in their evaluations have become critical. This study investigates whether LLMs exhibit implicit grading bias based on writing style when the underlying content correctness remains constant. We constructed a controlled dataset of 180 student responses across thre