Physicists Lose The Lecture

Tuesday, January 24th, 2012

Leave it to physicists to test whether lectures teach anything or not:

When Eric Mazur began teaching physics at Harvard, he started out teaching the same way he had been taught. [...] But then in 1990, he came across articles written by David Hestenes, a physicist at Arizona State. Hestenes got the idea for the series when a colleague came to him with a problem. The students in his introductory physics courses were not doing well: Semester after semester, the class average never got above about 40 percent.

“I noted that the reason for that was that his examination questions were mostly qualitative, requiring understanding of the concepts rather than just calculational, using formulas, which is what most of the instructors did,” Hestenes says.

Hestenes had a suspicion students were just memorizing the formulas and never really getting the concepts. So he and a colleague developed a test to look at students’ conceptual understanding of physics. It’s a test Maryland’s Redish has given his students many times.

Here’s a question from the test: “Two balls are the same size but one weighs twice as much as the other. The balls are dropped from the top of a two-story building at the same instant of time. The time it takes the ball to reach the ground will be…”

The possible answers include about half as long for the heavier ball, about half as long for the lighter ball, or the same time for both. This is a fundamental concept but even some people who’ve taken physics get this question wrong.

[...]

While most physics students can recite Newton’s second law of motion, Harvard’s Mazur says, the conceptual test developed by Hestenes showed that after an entire semester they understood only about 14 percent more about the fundamental concepts of physics. When Mazur read the results, he shook his head in disbelief. The test covered such basic material.

“I gave it to my students only to discover that they didn’t do much better,” he says.

The test has now been given to tens of thousands of students around the world and the results are virtually the same everywhere. The traditional lecture-based physics course produces little or no change in most students’ fundamental understanding of how the physical world works.

“The classes only seem to be really working for about 10 percent of the students,” Arizona State’s Hestenes says. “And I maintain, I think all the evidence indicates, that these 10 percent are the students that would learn it even without the instructor. They essentially learn it on their own.”

[...]

Mazur’s physics class is now different. Rather than lecturing, he makes his students do most of the talking.

At a recent class, the students — nearly 100 of them — are in small groups discussing a question. Three possible answers to the question are projected on a screen. Before the students start talking with one another, they use a mobile device to vote for their answer. Only 29 percent got it right. After talking for a few minutes, Mazur tells them to answer the question again.

This time, 62 percent of the students get the question right. Next, Mazur leads a discussion about the reasoning behind the answer. The process then begins again with a new question. This is a method Mazur calls “peer Instruction.” He now teaches all of his classes this way.

“What we found over now close to 20 years of using this approach is that the learning gains at the end of the semester nearly triple,” he says.

One value of this approach is that it can be done with hundreds of students. You don’t need small classes to get students active and engaged. Mazur says the key is to get them to do the assigned reading — what he calls the “information-gathering” part of education — before they come to class.

Comments

  1. Alrenous says:

    I once asked my physics 121 instructor if I could solve a particular problem in a way he hadn’t yet taught. Both in the sense of ‘allowed’ and ‘would it work’ His response? “Just do it [the way I was supposed to.]” As far as I can tell, most profs actively oppose understanding.

    I also gave informal understanding tests to my fellow students. There were two responses; the ones that liked the math but not the physics, and the ones that liked neither. Getting physics undergrads to discuss physics outside of homework is, apparently, like pulling teeth.

    This article makes me suspect that the problem is that the students are following the examples of the professors, and if you changed the classroom structure to be about learning instead of not-learning, you’d get more students appreciating the material.

  2. William Newman says:

    Alrenous wrote (using a physics professor as an example) that “as far as I can tell, most profs actively oppose understanding.” I think this must depend fairly strongly on which field in which institution. It probably also depends on which decade in some cases. I have heard stories like Alrenous’ several times before, and I don’t think they’re made up. I’ve also heard even more extreme stories about instruction in other countries (China, India, and the Philippines) that turn out a lot of good students that end up studying in the US. But such stories are far from my experience with physics profs at Caltech in the 1980s and at Cornell ca. 1990.

    Even at Caltech, I ran into cases of students who seemed too willing to use formulas without thinking too carefully about the principles than involved. But the physics professors at both schools seemed pretty consistently motivated to motivate particular analyses or approximations to ground principles. The only exception I remember is a cookbook-ish treatment of frequentist statistics in one section of a mathematical methods of physics course at Caltech.

    Incidentally, I’m not sure “informal” is the right word for what you describe as informal understanding. To me “informal” sounds like a category big enough to include silliness like informal arguments from relativity or quantum uncertainty to conclude that we can’t really know anything, or informal arguments from the second law of thermodynamics to conclude that evolution is impossible or that agricultural production must fail much faster than the Sun because terrestrial “low-entropy stocks” are somehow irreplaceably depleted despite the entropy flow from the Sun through Earth and back into cold space. My guess is that you mean a category narrow enough that it excludes such nonsense, perhaps “reasoning from formal principles which is rigorous but which doesn’t happen to require substituting numbers into algebraic formulas”. Examples of what I’m guessing you mean include (i) the classic tethered-balls thought experiment critique of Aristotle’s theory of falling bodies and (ii) (the missing understanding on display in) heavy boots. I don’t know the right term for that, but “informal” seems like the wrong term.

    (Wikipedia’s thought experiment entry gives a citation to Galileo’s Discorsi e dimostrazioni matematiche for the tethered-balls critique, but IIRC the basic idea is at least a century older than that.)

  3. Alrenous says:

    The heavy boots thing seems like it was spread with a tailwind of intentional effort. I seriously doubt it occurred independently to so many.

    For balance I should mention my electrodynamics 400-something prof, who, upon being asked about a particular symbol/concept, ended up taking me on a tour of his lab. He had a pretty cool lab.
    He was surprised I hadn’t seen the concept before, I told him I skip lots of class, but hadn’t seen it on any tests and such.

Leave a Reply