Dan Crowe already made the major point that I would like to make. I'll
expand it a bit more.
I believe the grading system that works the best is a final percentage
that is the weighted average of the percentages on various kinds of
work.
In my classes the exam average is weighted 3, lab average is weighted 2,
and problem-set average is weighted 1. That means the exams are 50% of
the final grade, the labs are 33%, and the problems are 17%. I have
sometimes played with the weights, but this is what I am using right
now.
With this system, as soon as you have one exam, a lab report, and a
couple problem sets, the student can easily see where their grade is
headed, and which area might need improvement. In a total-points
system, as Dan said, the problem set points and lab report points grow
(between exams) and make it appear the student is doing better and
better, then when the big-point exam comes, and the student does less
well, the grade suddenly drops.
In the weighted percentage system suppose the student gets 70% on the
first exam, has a 90% average on the first couple labs, and a 95%
average on the first several problem sets. According to my weights, the
total weighted average is about 81%. Between the first and second exam,
if the student continues to turn in problem sets that are running 95%
and lab reports that are running 90%, then her grade doesn't change one
bit during that time. By contrast in a total point system it will
appear the grade is increasing, then if the student gets another 70% on
the next exam, the grade will drop back to what it was after the first
exam.
It's possible to have a combination of total points and weighted
percentages, and I do this most notably with problem sets. Some of my
problem sets have 3 problems and some have 8. It might make sense for
the 8-problem set to count more. Thus, I record "points out of possible
points" for each problem set. The student has to keep a tally of their
total points and the total possible points in order for them to figure
their problem set percentage. But no matter how many problem sets and
problem-set points there are, the overall percentage on the problem sets
will still represent 1/6 of the final grade. I don't have to worry
about how many problem sets I have, nor how many points are on each set.
I just assign problems as I see fit, and some of them take longer and
some don't.
On the other hand, all my labs are the same value, so I can just record
the a percentage grade for each lab report. All my exams are also worth
the same. I don't want any one exam to count more than the others. So
I just record the percentage for each exam.
This system makes it very easy for the students to see where they are,
and it is easy to apply. It's also somewhat sad that they don't change
much throughout the term. Students tend to be pretty consistent on
their problem sets, and these run high because they can get assistance.
After the first lab report, where some of them learn that they need to
follow directions, the lab grades tend to settle into a consistent
percentage. And the by the second exam you pretty much know where the
3rd and 4th exam are going to be. The best way for them to improve
their grade is to do better on the exams, but they seldom do.
Michael D. Edmiston, Ph.D.
Professor of Physics and Chemistry
Bluffton University
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu