Evaluation techniques for Allen Downey's classes

The purpose of this page is to explain how I assign grades in my classes, and to make it easier for students to get an idea how they are doing as the semester goes on.

Most of my classes involve exams, graded homeworks, and quizzes. These activities are graded with different scales, explained below, and at the end of the semester, the final grade is determined by a weighted average of the total scores in each category.

As an example, imagine that there are 10 quizzes graded out of 10 points, 12 homeworks graded out of 10, and 3 exams graded out of 100.

That means that there are 100 possible quiz points, 120 possible homework points, and 300 possible exam points.

Also as an example, imagine that the weights for each category are 20% quizzes, 30% homeworks, and 50% exams. In that case, the total score for each student is:

quiz / 100 * 0.2 + homework / 120 * 0.3 + exam / 300 * 0.5

At the end of the semester, I calculate all the weighted totals and then sort, putting the students in rank order.

Generally, the median score gets a B. Occasionally I will adjust that score up or down, if I have a strong sense of what quality of work can be expected, and if the class as a whole either exceeds that expectation or fails to meet it.

To get an A or A-, you generally have to be one-half of the interquartile distance above the median. The interquartile distance is the difference in the scores of the 25th percentile and the 75th percentile.

Similarly, the line between C and C-, which is the threshold for credit-non, is usually one-half an interquartile distance below the median.

The line between D and F is usually one full interquartile distance below the median. In some cases I will override that rule if a student passes a comprehensive final exam. In that case, "you pass the final, you pass the class."

I use statistics like medians and interquartile distances because they are less sensitive to the effects of outliers than alternatives like the mean and standard deviation.

Quiz and homework scores

Quizzes and homeworks are graded out of 10 points. In most cases, these scores are determined relative to the performance of other students. My goal is to give different scores to work that is substantively different. This approach yields scores with the greatest discriminatory value.

You should resist the temptation to translate every quiz and homework score into a letter grade. These scores are not meaningful at that level of detail.

After the first few quizzes, you can get more meaningful feedback by looking at your total scores relative to the rest of the class. I will provide this information after each exam.

If you get a low score on a quiz, you should focus your attention on understanding whatever material you missed. Try not to waste emotional energy on scores that will have a small effect over the course of a semester.

Exam scores

Exams take a lot of time, including the time it takes me to write and grade the exam, the time it takes you to study, and the class time we spend taking the exam. I think it is important to use that time effectively. Therefore, I use exams as an opportunity to extend the material we have covered, and sometimes even introduce new material.

Exams are not just rehashes of homework and quiz problems. They require thought and the ability to think on your feet. Exams are part of the educational process.

Of course, if the exams are a bit more challenging than what might be the norm, I expect scores to be a bit lower. For almost every exam I have written in more than 12 years of teaching, the median score has been between 70 and 80.

I always write new exams and almost never reuse problems from previous years. I do that in part in order to be fair to people who don't have access to previous exams, and in part to bring greater creativity and interest to the course material.

What all this means, though, is that it is not always possible to interpret exam scores according to the numbers. If the median is a 72, then a 78 should probably be considered a B+, not the C+ it might get in a standard curve.

When I announce exam scores, I present the entire distribution of scores, so that students can see exactly where they fall in the distribution. Knowing where you stand relative to your classmates is the best indication of how you are doing.

Should I take this class Credit-Non?

The short (maybe rude) answer to this question is that I don't care. It has no effect on how I treat a student during the semester or how I grade at the end. If you don't want to give me the card telling me your status, you don't have to. I would just as soon not know.

If you are concerned about passing the class, and you need the credit, then you should almost certainly not take the class credit-non. Under the normal grading scheme, a D is a passing grade. Under credit-non, you need to get a C or better to get credit. If you are on the border of failing, the last thing you want to do is raise the bar.

Other than that, I don't really have advice. The decision to take a class credit-non is administrative, not academic. The only information I can provide is how you are doing in the class.

I am happy to provide that information at any point in the semester. If you come to my office, I can look over the grade sheet and tell you how your performance compares to your classmates. And I can give you very rough information about what your grade might be, based on your scores so far. But it is very hard for me to predict future grades.

I hope that helps.

What does my grade mean?

Your grade is my best effort to evaluate the quality of the work you present to me. I try to do that fairly, in the sense that I don't let irrelevant factors affect my evaluation, and accurately, in the sense that I don't misrepresent the quality of your work.

I understand that there are a lot of reasons a student might have trouble in a class. Maybe there is something going on in your life that is demanding your attention. Maybe you are really good at something else, but not very good at this. Maybe now isn't the right time for you to work with this class material, or maybe you're just not that interested.

If you are having trouble in my class and you want to tell me why, I am happy to listen, even if there is nothing I can do about it. If you don't want to tell me about it, you don't have to.

Since I usually don't know why a student is doing badly, I make a conscious effort to avoid guessing. If you are having trouble, you should know that I don't think you're stupid, and I don't assume that you are not doing the work. I only evaluate the quality of the work you present to me; I don't use academic performance to judge you as a person.

Some of my favorite students have gotten some pretty bad grades, and a few times I have given and A to someone that, frankly, I would have liked to see fail. So, if you don't get a good grade, it doesn't mean I don't like you, and it doesn't mean you're a bad person.