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You've always averaged grades. Your teachers averaged grades when you were in school and it worked fine. It works fine for your students.
Does it? Just as we teach our students, we don't want to fall for Argumentum ad populum: something is true or good just because a lot of people think it's true or good. Let's take a look at the case against averaging grades.
Hiding Behind the Math
Just because something is mathematically easy to calculate doesn't mean it's pedagogically sound. The 100-point scale makes averaging attractive to teachers, and averaging implies credible, mathematical objectivity. However, statistics can be manipulated and manipulative in a variety of ways.
One percentage point is the arbitrary cut-offbetween getting into or being denied entrance into graduate school. One student gets a 90% and another gets an 89%: the first is an A and the second is a B, yet we can't discern mastery of content to this level of specificity. These students are even in mastery of content, but we declare a difference based only on the single percentage point. The student with 90% gets scholarships and advanced class placements and the student with 89% is leftto a lesser path. Something's wrong with this picture.
Early in my career, one of my students had a 93.4% in my class. Ninety-four to 100 was the A range set for that school, so he was 0.6% from achieving an A. The student asked if I would be willing to round the score up to the 94% so he could have straight As in all his classes. I reminded him that it was 93.4, not 93.5, so if I rounded anything, I would round down, not up. I told him that if it was 93.5, I could justify rounding up, but not with a 93.4.
I was hiding behind one-tenth of a percentage point. I should have interviewed the student intensely about what he had learned that grading period and made an executive decision about his grade based on the evidence of learning he presented in that moment. The math felt so safe, however, and I was weak. It wasn't one of my prouder moments.