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18 March 2014

Bad Graphs: Everyone's students make them

What I expect a graph on a lab question to look like
Being a relatively new teacher is like being a new parent.  Everyone gives you advice, whether they have the requisite experience (or success) that would make that advice valid; everyone thinks they can do your job better than you.  Moreover, even those giving reasonable advice neglect the fact that you are likely overworked and underslept in your new position.  You're happy just to survive the next class/feeding without falling over; getting everything just right the way your mentor or your mother would do it is beyond your capability right now.

And that's fine.

Certainly you should listen to advice from experienced teachers who have earned your respect.  But too many new teachers, like too many new parents, live in mortal fear of failing to live up to expectations.  Face it -- you're gonna screw up.  And that's okay, because every other teacher and parent in history has screwed up, too.

Exempli gratia:  I put together a series of posts about "bad graphs" at the request of numerous readers.  Some, such as the "dot-to-dot," "nonlinear axes," or "fudged line" bad graphs, represent horrid mistakes.  In my summer institutes, I am emphatic that it is our responsibility as physics teachers to do enough lab work that students don't even think to make such mistakes.  A best-fit line should be drawn properly with a ruler, as shown in the graph at the top of this post.

So are you a naughty, naughty teacher if a student makes a graph like the one below on an exam?
Look at how this student fudged his best-fit line
so that it would touch every data point.  BOUX!
Well, if at the end of the year virtually every student in your class connects data dot-to-dot or fudges his best-fit lines, then that's not a good thing.  When exactly did you do your lab work?  

Oh, that's right... in your first year, you were lucky to think up one or two good lab exercises.  And on top of everything else going on, that's all you did, just a couple of labs.  No wonder your students couldn't make an appropriate graph -- they didn't have enough practice.

So relax, and learn from the mistake.  This summer, plan some more lab exercises.  And now that you kinda know how a school year works, be sure you actually do those exercises.  Hold the students accountable for making their graphs correctly in class.  You'll be surprised at how quickly you manage to stamp out silly mistakes once you have the time and energy to focus on them.

If only one or two students out of 40 commit the sin of a bad graph under the pressure of the exam*, don't even worry about it.  You're not disappointing anyone.  Your mom isn't going to give you the look of withering scorn... she'll save that for when you listen to your pediatrician instead of to her quaint folk wisdom.

*Or because that particular student never listened, no matter how hard you tried to make him

Oh, and where did I get that bad graph?  Trimester exam last week.  My student.  One of two -- the other did the dot-to-dot thing.  Guh.  But I don't think I'm getting sacked.  Point is, it happens to all of us.

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