Here's a breakdown of common types and how they work:
* Adding points: The simplest method. A fixed number of points is added to everyone's score, or a percentage is added. This raises all scores, potentially inflating grades that were already good and also helping students who did poorly.
* Curve based on standard deviation: This method uses the mean (average) and standard deviation of the class's scores. Grades are assigned based on how many standard deviations a student's score is from the mean. For example:
* Within one standard deviation of the mean might be a B or C range.
* One to two standard deviations above the mean might be an A range.
* One to two standard deviations below the mean might be a D or F range.
* Scores further from the mean are scaled accordingly.
* Curve to a specific distribution: The instructor might aim for a specific grade distribution (e.g., 10% A's, 20% B's, 40% C's, 20% D's, 10% F's). The scores are then adjusted to fit this pre-determined distribution, regardless of the actual performance.
* Curve based on highest score: In some cases, the highest score is set to 100%, and other scores are adjusted proportionally. This method is particularly sensitive to the highest score and is viewed as unfair if that score doesn't represent near-perfect mastery.
Arguments for Grading Curves:
* Account for test difficulty: If a test proves unexpectedly difficult, a curve can mitigate the impact on students' overall grades.
* Maintain a consistent grade distribution: Some instructors believe that a certain distribution (like a bell curve) is appropriate for their course.
* Motivation and morale: Curves can sometimes boost students' morale, particularly if the majority scored lower than anticipated.
Arguments against Grading Curves:
* Unfairness: A curve can arbitrarily lower the grades of high-performing students, even if they demonstrated excellent understanding of the material. The score they earned is changed to fit a curve which they had no control over.
* Lack of transparency: Students might not understand how their grades were adjusted, leading to confusion and frustration.
* Focus on relative performance, not mastery: Curves emphasize competition amongst students rather than individual learning and achievement. A student might receive a good grade despite a significant lack of understanding.
* Distorts the meaning of grades: A grade is intended to reflect what a student knows. A curved grade obfuscates that.
In summary, while grading curves might seem like a way to "help" students, they are a controversial practice that should be considered carefully due to the ethical and pedagogical implications. The best practice is often to carefully design assessments that accurately measure student learning, and grade based on the actual performance on those assessments.