So what's the most effective way to grade high school math courses? I've gone through a variety of methods throughout my teaching career, either determined by the math department at whichever school I happened to be employed by at the time, or driven by whatever might be fashionable in current educational development readings.
Here's a breakdown and my critique of some of my current or former grading scales. Most of the schools in which I've taught did the traditional A, A-, B+, etc.. letter scale, though use of this scale could lead to a side-topic of it's own!
At one school the minimum passing grade was 70% - anything less and you failed. After failing an Alg 2 student with a 69% one year, my principal informed me that since I was good with numbers I should adjust scores so that no one in my classes scored between 65 and 69% ever again - they were either above or below! At one time that same school would not allow a student to get a "minus" score: B+ and B were allowed, B- wasn't. So scores or 80-86 were all B's, while 87-89 got B+, and a 90 was an A. No focusing on minuses, which lead to negativity.
I do not like my school's current grade scale - 87-89 is a B+, 84-86 is a B, but 80-83 is a B-. Why does the B- take up 40% of all the B grades, but the B+ and straight B get 30% each? Shouldn't the B+ and B- get 30% each, and the straight B get 40%? So 80-82 would be a B-, and 83-86 would be the B. One of my old districts graded this way. When I suggest this to current math students, they understand the unfairness immediately, but no change has been forthcoming. I think it is due to certain teachers not wanting to award an A for 93% in a class - they want a minimum of 94 or even 95%. Anything to make things tougher for kids.
Back on topic - how to grade. When I first starting teaching I gave category scores - 50% of the final grade was based on tests, 25% on quizzes, 20% on homework, and 5% on participation. That 5% participation grade was held over the heads of the kids that skipped frequently, though whether we should grade on attendance is another story. I immediately found a problem with this scoring system: a student could be failing a class with a 58%, fail a final test with a score of 54%, but suddenly have a passing grade of 60% in the class. If the student's test average was very low (say 45%), the final test of 54% would raise their test average, thus raising their overall class average enough to have the student receive 60% in the class. I didn't like this ironic outcome, so I changed my scoring system to strictly be based on total points.
Using total points is my favorite method of grading - tests are worth 80-100 points, quizzes 10-25 points (usually 20), with homework 2-5 points, usually 3. You get a test score higher than your class average, your overall grade goes up. You get a score lower than your average, your overall grade goes down. The only problem is that the scoring levels are not consistent year to year or even term to term - your final grade could be based anywhere from 45 to 65% on test scores, depending on when tests were given.
My current school technically requires percent scores (final grade is 4% participation, 12% HW, 24% Quizzes, 40% Tests, 20% Final Exam), but now we have a thing called cumulative scoring, which takes the philosophy that "we don't care what you did along the way, we only care about the final results," the final results being what you did on your final exam, even though the final exam can only question roughly 50-60% of all the material covered. Our tests are supposed to be cumulative as well - a Unit 2 test would be 50% unit 1, 50% unit 2, while a unit 5 test would be 20% unit 1, 20% unit 2, ..., 20% unit 5. So theoretically, your final test would cover the same material as your final exam. If a student has 100% (or close) of their homework completed, they could replace all previous tests with the score from their last test, assuming it is their best score. This worked great when we had 75 minute class periods last year, but cumulative testing is nearly impossible in a 55 minute time period (our current class schedule.) Plus, is the final test the only thing? Outcomes only? How about those that participate in the mathematical process throughout the year, but have a bad day during the final exam?
No easy answers, but a lot of questions raised when it comes to scoring.