To a person with a hammer, everything looks like a nail.
Here are some examples that I’ve seen in classes:
- After you teach algebra students how to multiply polynomials, some can suddenly no longer add polynomials and will multiply an expression like (x + 3) + (x – 4).
- In Calc II, I first teach how to use substitution to create new power series for functions. Later, I teach how to find a Taylor series. On the test, I always ask students to demonstrate finding some power series using the known series. But for many students, once they learn the Taylor series, it is the hammer they apply to everything.
- In Calc I, students learn how to find derivatives using the power rule first. Later on, once they learn the quotient rule, they will try to find the derivative of 4/x using the quotient rule, rather than just rewriting the expression and using the power rule (which was the first, and simpler method).
For algebra, I’ve recorded hundreds of these types of hammer & nail issues in the Instructor Resource Binders I recently authored in the Instructor Tips that are included with each topic. Once you know that the issues exist, you can try to change the hammer-and-nail thinking by continuing to present problems that make students think about alternate methods – or at least show them that using the most recent “hammer” is not the best way to do the problem. After seeing this enough times, the hope is that the students will begin learning to think for themselves.
One of the reasons that I love using the methods I outlined in “Back to the Board” is that I can instantly see which students that are trying to rotely apply the latest learned technique, and throw out new problems that use other techniques or tweaks until I see that they are no longer “thinking with a hammer.”
SIDE NOTE: These little 10-minute talks at conferences drive me crazy. Ten minutes is barely enough time to introduce a topic. If conferences are really going to use this format, then they should be sophisticated enough to have a website where presenters can link to a longer-format presentation that is hosted online. For some presenters, that might mean a set of slides from a longer presentation, and for others, it might be a recording (with slides) of the actual longer presentation. I just get annoyed with getting a 10-minute teaser and then not having instant access to the rest… which is why I always post my presentation prior to presenting. Just like our students, the best time to gain the attention of the audience is when they are interested in the topic – like when they go back to their room after the presentation.
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