There’s an insidious misconception that the ability to reliably get the right answer to a question must be evidence that the student thoroughly understands the topic.
The biggest challenge I have this year is with my AP Chemistry students. All of them took honors Chemistry I last year, and all of them had an “A” average in the course and enjoyed it. The teacher they had last year is widely considered to be a good teacher, both by students and by my colleagues in the science department. She has mnemonics for every topic, and her students are quickly able to recall most of the mnemonics and applicable formulas. Like most states, Massachusetts spells out the Chemistry I curriculum, with a list of eight major topics and a total of about forty subtopics. The benchmark is the state’s high-stakes MCAS test, in which each question has a one-to-one correspondence with exactly one of those forty subtopics, and each question has a one-step answer or solution that requires at most one formula applied in the most obvious way. None of the questions on the MCAS exam combine topics or require multi-step solutions.
This teacher’s students memorize the appropriate formulas and mnemonics and apply them blindly, because their goal is to earn good grades. Getting the right answers is the best route to that goal, and a blind formula that always works is more reliable than potentially over-thinking the question. (In fact, last year one of my students confessed that she and her fellow honors Chemistry I students would regularly conspire to intentionally miss a couple of questions on each of the tests, so the teacher wouldn’t be tempted to make the tests more challenging.) These students were never made to demonstrate in-depth understanding of a topic, and they had never encountered questions that couldn’t be answered by application of a simple formula.
Now that I have them in my AP Chemistry class, I’m insisting that they tackle multi-step problems and problems that use concepts in ways they might not have seen before. Because these students had always used the mnemonics and formulas as shortcuts and were never made to solve problems that went beyond those formulas, they don’t know where to begin. At the beginning of the year, my students were using 1 mol = 22.4 L to solve molarity problems, because when they studied mole conversions, they were given problems at STP and were taught to always use 22.4 L whenever they saw liters in a problem! These students can only do mole-mole and mass-mass stoichiometry problems, because those are the only ones they’ve been taught.
In short, I spend most of my efforts trying to undo the damage of of “Memorize this formula and use it,” because my students have taken that to mean “Memorize this formula and apply it blindly as a substitute for learning the science behind it.”
Originally posted to the ChemEd-L discussion list.
