This paper analyzes the impact of grading practices on the gender gap in student achievement. We examine the gender difference in the difference between teacher grading and scores on national exams to test whether there are gender differences associated with different grading systems. We use data on 21 subjects across humanities and sciences for students taking exams between the 4th and 12th grades from 2007 to 2018 in Portugal. Our results indicate that a grading system based on exams favors boys, while one based on teacher assessment favors girls.