Grade inflation is pervasive in American high schools. Is rampant grade inflation cause for concern? How teachers' grading standards affect student success is an empirical question--one that the author addresses in this article in a new study of roughly 350,000 North Carolina students taking Algebra I between 2006 and 2016. The author first measures the grading standards of individual Algebra I teachers in the state by comparing the course grades they assigned their students to those students' scores on a standardized end-of-course exam. The author then asks whether students did better or worse than expected when they were assigned to a more-demanding teacher. The results confirm that "everyone gets a gold star" is not a victimless mentality. Not only do students learn more from tougher teachers, but they also do better in math classes up to two years later. The size of these effects is on the order of replacing an average teacher with one near the top of her game.