I don’t know why my G-Chem 1 students, on average, did much more poorly than expected on the most recent midterm that covered stoichiometry. While the midterm exam average for stoichiometry is typically lower than the other midterms, this year it was substantially lower, far outside the norm.
Last year, my G-Chem 1 exam averages were similar in the first three midterms, so I think the range of academic ability in chemistry is similar between the two classes. I also have all four midterms at the same point during the semester (although there was minor moving around of topics). So, it shouldn’t have been Thanksgiving break that caused students to forget everything they learned. And some students still aced the exam. I even made sure to cover the last bit of stoichiometry the Friday before Thanksgiving break so that the many students who chose to miss Monday’s class wouldn’t miss the last section on redox reactions.
What’s different? The main change I made in my G-Chem class was to ditch the online homework system and its accompanying textbook. Instead, I assign some homework and “collect” a subset of it to grade. What I collect is clearly less than what I had previously assigned in an auto-graded online homework system. It’s possible that students are not doing the other suggested problems that I don’t collect. (Some certainly do, when they come in with office hour questions or turn some of it in even if I didn’t assign those as part of what I collected. But others might not.) But the questions I do assign are written the way I would write an exam question, so I felt that was helpful to students. This is unlike the auto-graded online homework system that often phrases questions differently.
None of this seemed to be a problem through the first three midterms. Students were doing similarly as they did in the past. I even asked for feedback from the students about how they felt about the changes I made and the majority seemed to like them and thought my study guides were helpful to learning the material. My current hypothesis for the difference is that when it comes to stoichiometry, the students need much more practice problem solving, and the changes I introduced caused at least half (or more) of the class to practice less compared to previous cohorts. This wasn’t as big a deal in earlier topics. Even though there were calculation type questions earlier in the semester, they weren’t as concentrated as when we covered stoichiometry.
I think I need to assign more problems or provide more time in class to work through them if I don’t want to be doing more grading. And given that I’ve jettisoned the textbook, I should move stoichiometry earlier. (We’ve been using “atoms-first” textbooks for many years that shift stoichiometry to the last third of the semester. I didn’t want to make too many major changes compared to what I did last year.) I also think the Thanksgiving break causes students to forget what they learned, but I suspect this wreaks more havoc for stoichiometry than other topics, and this year there was a double whammy when the students didn’t practice enough.
Thankfully for the students, I drop the lowest of the four midterm scores, and that will be the case for the majority of students in my G-Chem class this semester. That was also true last year (stoichiometry always has the lowest average), but the average scores were nowhere as low as this year. So the overall student grade hasn’t been impacted yet, but it may mean that many students need to beef up their stoichiometry problem-solving skills before the final exam. While the final exam is cumulative, so stoichiometry might be 20-25%, that’s still a substantial portion. Some students have come by to talk, now that they realize what they missed so that’s a good sign. Hopefully more do so.
There are two other possibilities for the lower-than-expected exam scores. It’s possible the exam was harder this year. I don’t actually think so, but since instructors are inflicted with the curse of knowledge, I can’t say for sure. I’ve been writing exams for many years and I’m confident that the exam I wrote was about right, but it could have been a tad harder – certainly not so much more difficult to cause the substantial drop in scores. It’s possible I have an academically weaker class this year when it comes to stoichiometry and math-related chemistry problems. My G-Chem classes are small, often less than 30 students (although it can be as high as 40) so there can be substantial differences from one group of students to another.
In any case, I need to think about some changes I’d like to make to my G-Chem 2 class next semester that is certainly more math-heavy. I am teaching the Honors section and the students who register for that class are self-selecting so I might not run into the same issue. Certainly I need to make changes to my G-Chem 1 class next year if I continue not to use an online homework system and textbook.
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