At schools with low grading standards, students receive higher school-awarded grades across multiple courses than students with the same skills receive at schools with high grading standards. A new methodology shows grading standards vary substantially, certainly enough to affect post-secondary opportunities, across high schools in Alberta. Schools with low grading standards are more likely to be private, rural, offer courses for students returning to high school, have smaller course cohorts, have a smaller percentage of lone parent households and a larger percentage of well-educated parents. Variation in grading standards changes post-secondary opportunities in systematic ways.