How weighting is used to calculate grades is not always clearly understood by students and parents. This explanation should be helpful. In the example, there are three weighted categories: Homework, Tests, and Final. Each is weighted 30%, 50%, and 20% respectively.
The figure to the right illustrates that a student's averages for the Homework and Tests categories are 60% and 70% respectively. Since there is no score for the final exam, that category will not be used in calculating the student's average
The weight of each category used is multiplied by the student's average for that category. Those products are summed together and divided by the total of the weighted categories in use (80% as pictured above). In this example, the student has earned 53% of a possible 80% for an average of 66.25%. How that percent grade converts to a letter grade is based on your grading scale.
Q: How can a student's grade go down when they get a high score on an assignment?
A: Remember that grades are weighted by category. So if the score on the assignment is lower than the average for that category, the overall grade will go down.
Example: A student’s current overall grade is 90% for all categories (tests, homework, etc.) and they get a 92% on the next test, intuition tells us that their grade should go up. However if their test average is 95% then the weighted average for the Tests category will go down and therefore their overall grade will go down as well.