How Are Exams Factored into the Students' Grades?

Semester exams count for 20% of the students' semester grades.  The semester grade for a class is composed in the following way:

40% - Quarter 1 grade
40% - Quarter 2 grade
20% - Semester Exam grade

Last year, we conducted a comprehensive study to examine the impact that exams have on students' semester grades.  We looked at the possibility of exam exemptions and changing the weighting of exams.  In the end, we decided to keep our current 20% weighting of exams, and we implemented an exam exemption policy for second semester seniors.  The main findings of our study were that exams tend to have a negative effect on semester grades (for about 2/3 of the students), but the effect is very small on average.  The average decrease is 0.71 points (on a 100 point scale), and 54.5% of the semester grades changed by less than a point due to the grade on the semester exam.  Here is the full Summary of the data collected on Semester Exams and their impact on Semester Grades.