Students in the physical sciences--physics and chemistry--often take multiple-choice exams for introductory courses. Some students will write a lot on their exams, while others write very little. Does the student doing more scratch work on their exam perform better than one who does not write as much? We analyzed multiple-choice exams in physics and chemistry, measuring the amount of student writing on each exam, and explored the correlation between scratch work and exam grade. We conclude that, on average, successful students write more on their exams than unsuccessful students. Faculty should model problem-solving strategies that involve writing and drawing to increase a student's propensity for success.