When educators see that two students received a B in a particular course in two different schools and/or years, does it indicate the same level of understanding and achievement for both students? This paper addresses the assumption that grades are equivalent within subjects across schools and years. By comparing course grades to a standardized test score that is comparable across all schools, districts, and states, this relationship is investigated. Data used in this study include public high school student records from one diverse state in the continental U.S., along with corresponding exam score records from the College Board. To explore grade inflation, where grades increase without corresponding increases in achievement, cumulative high school grade point averages are measured across time and compared to changes in the math (SAT-M) and verbal SAT-V) sections of the SAT[R]. To measure grade non-equivalence across schools, five Advanced Placement Program[R] (AP[R]) subjects were chosen for comparison across five large high schools. The AP Exams serve as a standard measure of skills and knowledge obtained by the student. They are compared to AP course grades, which are assigned by individual classroom teachers and based on a variety of criteria at the teachers' and schools' (and possibly districts') discretion. Results indicate a presence of grade inflation across years and non-equivalence across schools. (Contains 3 figures and 7 tables.)