# Lose 25 Points in 25 Seconds

When I give tests/exams to my physics students, the tests are usually comprised of problems that range from straightforward to a little challenging to very challenging.  I let them use their notes, textbooks, old homework assignments, and anything else on paper  (except for questions and answers that are specific to the test).  If they get stuck, I help them get unstuck during the test.  It does lead to a high percentage of high grades, but the trade-off is that students make a lot of mental connections during the test, which means the test itself is contributing to their learning, as long as they actually do the work themselves.

To combat cheating, I distribute at least three different versions of each test.  Usually, the questions are the same, but the numbers are different.  If I see a number from another version of the test on someone’s paper, I know the person cheated.  First-time offenders get zero points for any question that appears to have been copied.  Second-time offenders get zero points for the entire test.

I warn the students about this at the beginning of the year.  I explain about the different versions with different numbers in the problems.  Then I secretly write a 3-digit number on a piece of paper and offer an “A” on the first test to any student who guesses it exactly in one try.  So far, no one has guessed the number.  (With total student loads ranging from 130-160 students, I would expect one student to guess correctly every seven or eight years.)  After they all make their guesses and I reveal the number, I explain that if their answer contains numbers (in the work or in the answer) that appear on another version of the test but not on theirs, they lose all credit and I’m not going to believe any explanation that claims that they just wrote down a number randomly and happened to get unlucky.

Nevertheless, every year I catch a few students cheating this way.  The latest case was on a 3-step problem (worth 25 points out of 100) that required students to calculate the net force on an object from a word problem that gave them the applied force, the mass, and the coëfficient of friction.  They had to:

1. calculate the normal force,
2. calculate the force of friction, and
3. subtract the force of friction from the applied force.

One student had done the entire problem correctly and gotten the correct answer.  Then, underneath his answer, which was something like 137.5 newtons, he wrote “Net force = 231.6 newtons,” which had nothing to do with the numbers on his paper, and which happened to be the correct answer to the same question on a different version of the test.

This little addendum cost him the entire 25 points.

A funnier story came from my second year of teaching.  If a student gets a nonsensical answer, I give them one point of partial credit (in addition to any other partial credit they might have already earned) for telling me why the answer doesn’t make sense.  (However, if they get a correct answer and try to tell me that it doesn’t make sense, it costs them a point, to prevent the problem of a student claiming that every answer doesn’t make sense, just in case.)  One student wrote “Doesn’t make sense because the answer should be 11.3.”

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## About Mr. Bigler

Physics teacher at Lynn English High School in Lynn, MA. Proud father of two daughters. Violist & morris dancer.
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### One Response to Lose 25 Points in 25 Seconds

1. Ezra Peisach says:

I also appreciated the concept of getting the wrong answer – and knowing it was the wrong answer. I have received credit for that in the past – and it usually was after some derivation and then to discover the units were wrong when I started putting in numbers- “I know the answer is wrong as the units should be meters not meters^2″