Grading and xkcd

Today’s xkcd comic nails the problem with averaging customer ratings. The connection to grading is pretty obvious.

Couple this with parachute packing:

And do we really need anymore reasons to convince people we need to switch to Standards-Based Grading?

Also see these two articles from ASCD (in case blog posts don’t fly with your audience):

27 responses to “Grading and xkcd

  1. I’m with you on switching to standards based grading, in fact all of our elementary students in my district are graded that way. I think any roadblock to this at the secondary level would come from universities and colleges looking for GPAs; how would standards based grading translate to college entrance forms?

    • You can still create a GPA and maintain solid grading practices. Often people see meaningful feedback and numbers as polar opposites, but they can work together. See

  2. As I said in response to David Wees’ post (, the point here is not that it’s necessarily wrong to rate things through averages, it’s that all evidence is not created equal.

    The five stars for “Alert Options” should not be given equal weight as the one-star for “Tornado Detection Failure”. Similarly, “Organized Notebook” and “Homework Completion” should not be given equal weight as, say, performance on meaningful assessments. I don’t know many teachers who do that, but maybe they’re out there.

    • Even though most teachers do not give equal weight, the fact that binders, HW, and participation are averaged in with knowledge pollutes the grade. With standards-based grading, the non-knowledge aspects would be reported separately. Video games, restaurants, etc. are rated in multiple categories (graphics and gameplay, atmosphere and food) to prevent the rating pollution that can happen as xkcd points out. Perhaps app should be rated in categories like UI, functionality, etc.

  3. Great post, it is something that I struggle with all the time. Everyone wants a number (I teach high school), but until all the evidence is in and properly weighted that number really has no value and should really be disregarded. I try to ensure that I give students the maximum benefit, but I always feel hamstrung by grading programs and policies that don’t seem to encourage that.

  4. It’s also good to note that in the parachute packing, Student B not only reached a high level, but made it look like a pattern. Also that student C was required to do the other 6 tries after a stellar first one. I think SBG can easily fall into the trap of a student getting a good grade then quit assessing that standard immediately so that the grade is frozen in the high position.

    • We do SBG at our elementary, as well as the school my daughter attends, and in both cases the standards are all present on the report card at the beginning of the year, and stay there throughout. Standards that haven’t been addressed yet are left blank, while those that have already been evaluated continue to be addressed, as my daughter actually slipped in a few areas as the concepts in a particular area got a bit more difficult, or was introduced to new information.

    • That is why teacher-initiated assessment should go back to old material frequently to gauge for retention. In my SBG system, scores can go down. Of course, the student can always assess again to show me they know it.

  5. What is everyone’s experiences with public perception of SBG? How hard is it to gain approval from administrators and parents?

  6. Another comic about issues with averaging long-term data in order to describe “current state” of growth/understanding: Cool to see xkcd tackling a similar issue! Thanks for tying it in to the power of standards-based grading.

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  8. Ha! Beautiful. I saw that comic but didn’t make the clever connection, though it’s obvious now in hindsight.

    It will be printed and posted in my classroom!

  9. Frank, my head is about to explode (in a good way!) – brilliant blog, enough ideas here for a master’s degree! Never really been a blog reader before, it had to wait until summer vacation for me to get into it. Now I’ve spent most of the last two months on the patio with my iPad reading through all your posts and the SBG blogroll and a bunch of other blogs – how can I NOT try SBG this year? My partner thinks I’m insane for spending vacation doing schoolwork, but I can’t wait to give this a try! I promise to give thoughtful, less gushy comment another time, but just finished my draft of physics standards at midnight last night and realized I’d never given any of you feedback for setting me off on this road. Cheers!

  10. Thanks for your ever insightful posts. I am off on this road this year. My dept chair is looking to it as a pilot program. I hope they don’t expect perfection from the start. I have my 1st grading period standards ready for both math and physics in grade 8. The English teacher is going the route of 3Ps so it should be an interesting start to the year. 🙂

    PS: I used the marshmallow tower with my grade 11 physics class today and it was interesting. Will discuss TED talk tomorrow.

  11. I would be interested to see more about how teachers grade labs. I recently read about people that give a lab test instead of grading the actual lab. During the test, students are allowed to use his/her own lab write up to help answer the questions. This seems like a great solution to me.

    Is there any source of lab-based questions available? (Or is ‘wheel inventing’ the only source)

    • I think the questions depend on the purpose of the lab and the concepts/skills you want to assess. I’ll give you some questions from a lab quiz I gave my conceptual physics class a while back:

      1. You are working as a stagehand for the school musical “Peter Pan.” In one scene, Peter Pan is tied to an invisible rope. He swings back and forth across stage like a pendulum. The director wants Peter Pan to swing back and forth more slowly.
      (a) Name one thing you can change so Peter Pan will swing back and forth more slowly:
      (b) Support your answer to (a) with EVIDENCE from your lab notebook:
      (c) Describe one thing that will NOT have any effect on Peter Pan’s swinging:
      (d) Support your answer to (c) with EVIDENCE from your lab notebook.

      2. You would like to use a pendulum metronome to keep the beat to the Beatle’s song “Hey Jude.” Using a stopwatch, you determine that the song makes 12 beats in 10 seconds. Currently, your pendulum metronome has a length of 70 cm and a mass of 85 grams.
      (a) Will your pendulum keep the correct beat? Support your answer with EVIDENCE from your notebook:
      (b) How could you change your pendulum so that it keeps the correct beat? Give specific numerical values! Support your answer with EVIDENCE from your notebook.

      3. When a green superball is dropped from a height of 150 cm, it rebounds to a height of 90 cm.
      (a) How high will the ball rebound when it is dropped from 200 cm? Show all your work!
      (b) Your friend drops her orange superball from a height of 100 cm and it rebounds to a height of 75 cm. Whose ball is bouncier? Show all your work!

      4. What relationship exists between how much paper towel was weighed and percent error? Support your reasoning with EVIDENCE from your lab notebook!

      5. The length of a $20 bill is 15 cm. When we did the $20 demo in class, no one was able to catch the $20 bill when the center of the bill was placed at your fingers.
      (a) When the center of the bill is placed at your fingers, what length of bill passes through your fingers when it is dropped?
      (b) Based on your answer to (a) what reaction time would you have if you could barely catch the edge of the $20 bill?
      (c) Based on your answer to (b), would the average person be able to catch the $20 bill? Use EVIDENCE from your lab notebook!

  12. Thank you very much for these questions. I will incorporate them into this lab test idea. I also want to share what I’ve learned and hope to do.

    From what I’ve read, the lab test is instead of grading labs. This saves an enormous amount of teacher time, has the student become responsible for understanding what the learning experience of the lab was providing, and responsible to write understandable lab reports.

    As I understand it, after 3 – 5 labs, the lab test is given with multi-step questions reflecting the lab experience. For example, if labs on constant speed, constant acceleration, freefall, friction, and equilibrium are being tested, these may be some of the questions on the lab test.

    1. Two cars start at the same time and move from left to right. [I don’t know if it will show up but a ‘dot diagram’ would be here.] The dots represent the location of the cars every second.
    a) Were the cars ever next to each other? If so, at what time?
    b) Which car was traveling faster? How do you know this?
    You are inside a cargo plane traveling at constant velocity. From the middle of the ceiling of the plane, you drop a ball and it hits the floor below. The ball hits the floor:
    a) exactly below the midpoint of the ceiling
    b) ahead of the midpoint of the ceiling
    c) behind the midpoint of the ceiling
    d) more information is needed
    A soccer ball is kick along the ground horizontally. What is its average speed if its displacement is 21 m after 4 seconds? (showing work)

    2. A student designs an experiment to determine the height of a building. After several trials the building was found to be 5.25 m high.
    a) How was the height of the building determined?
    b) If a ball is thrown off the building, how long would it be in the air before it hit the ground? (showing work)
    c) Draw a free body diagram of the ball in flight with air resistance present.
    d) Determine the terminal velocity (showing work)
    e) [Include a stroboscope photo here:]
    From the photo, how can you tell the ball is accelerating?
    f) Which would hit the ground fists if dropped from the building in a vacuum (no air resistance), a leaf or a nail? Explain your answer.

    3. [For this next question, a diagram of 4 freebody situations is included labeled a – d.] The following questions refer to the diagram and you may choose more than one for each question.
    a) Which diagram represents an object in equilibrium?
    b) Which diagram represents an object that is accelerating?
    Not referring to the diagram:
    c) If a nonzero net force is acting on an object, then the object is:
    1. at rest 3. being accelerated
    2. moving with a constant velocity 4. losing mass
    d) A 10 N force pushes a body northward while a 15 N force acting at the same point of the body pushed it southward. What is the result of these two forces? (show work)

    4. Given distance vs. time data:
    a) Using graphical analysis, find the mathematical relationship satisfied by the data.
    b) For the object undergoing this motion, find its position, speed, and acceleration when the time equals 10.3 seconds?
    c) On the graph, what specifically does the slope of the line represent?
    d) Determine the slope (showing work)
    e) Sketch a graph for what a speed vs time graph would look like for this motion.

    5. a) Describe the procedure you could use to determine the coefficient of friction between various materials.
    b) Write the equation for friction.
    c) What happens to the friction force as the normal force increases?
    d) Which coefficient is higher kinetic or static?
    e) Draw the freebody diagram for a block moving at constant speed across one of the tested surfaces and label all the forces.
    f) What is the net force on the block under this condition of constant velocity?

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