Research has revealed that girls have outshone boys in all school subjects for nearly a century.
The findings of the research may help break the stereotype that boys do better than girls in science and mathematics.
Grades of girls have been consistently higher than that of boys across several decades with no significant changes in recent years, said the study.
"Although gender differences follow essentially stereotypical patterns on achievement tests in which boys typically score higher on math and science, females have the advantage on school grades regardless of the material," said Daniel Voyer from University of New Brunswick, Fredericton, Canada.
Based on research from 1914 through 2011 that spanned more than 30 countries, the study found the differences in grades between girls and boys were largest for language courses and smallest for math and science.
The degree of gender difference in grades increased from elementary to middle school, but decreased between high school and college.
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The researchers examined 369 samples from 308 studies, reflecting grades of 538,710 boys and 595,332 girls.
Previous research has shown girls tend to study in order to understand the subjects, whereas boys focus on the final grades.
"Mastery of the subject matter generally produces better marks than performance emphasis, so this could account in part for males' lower marks than females," the authors wrote.
The study appeared in the journal Psychological Bulletin.