I wasn’t sure students were grasping my lessons—so I devised an experiment

From ScienceMag:

As a chemistry lecturer, I was never quite sure how much course material my students were truly absorbing, so I decided to embark on an experiment. At the end of one lecture, I gave each student an index card to write on. Then, I listed on the board the key topics I had covered and asked the class to copy them onto the cards and write green, yellow, or red next to each topic. Green meant “I understand this well,” yellow told me “I am somewhat unsure,” and red indicated a more dire problem: “I am confused or lost.” I wasn’t sure how the approach would work. I waited eagerly to collect and examine the cards, hoping for a comprehensive, real-time picture of how much my students actually understood.

Years earlier, when I first started to teach as a graduate teaching assistant, I simply gave my lectures and did not question whether my methods were effective. If no one raised a hand, I took it as a sign that the material was clear. But over time, I began to realize I shouldn’t make that assumption. After exams, I would discover concepts students had misunderstood, and I would wonder how I could have intervened earlier. Because students had to master some concepts before moving onto other topics, not catching problems early meant misconceptions compounded over time.

As a scientist, I was trained to seek evidence, test hypotheses, and adjust based on data. However, in the classroom, I was teaching without any feedback. It felt like speaking into the void, without an opportunity to make adjustments.

I needed a way to gauge students’ understanding before it was too late. I could have given regular quizzes to assess where they were in their learning. But what I really wanted to test was my own teaching methods, and I was looking for a low-pressure way to invite feedback. So, soon after I became a chemistry instructor, I started to experiment with the index cards. After each lecture, I would collect them and identify the topics with the most yellow and red comments.

The distribution of colors—what I refer to as “traffic signals”—was eye opening. Concepts I thought were straightforward showed an unexpected mix of yellow and red. For the first time, I had a snapshot of comprehension across the class, and it quickly transformed how I taught. I began to see lectures not as performance, but as an experiment that allowed me to test, adjust, and learn alongside my students.

Importantly, the yellow and red signals told me I needed to slow down. After one lecture that included a concept called freezing point depression, it became clear that many students were struggling to understand the idea. Some had green responses, but most were in the yellow and red. So I began the next class with a targeted review and a real-world example: why salt lowers the freezing point of water on roads. I also made a point of telling students then and during other lectures that if they still had questions about the yellow and red topics we reviewed, they were welcome to stop by during my office hours for additional help.

When the COVID-19 pandemic hit and teaching moved online, I could not use physical cards, so I developed a digital version. At the end of each lecture, I displayed the key topics on my shared screen and asked the students to send me a chat message with their level of understanding for each topic. For example, a student might send a chat message that read “green, green, red, yellow, green.”

As I continued to use the cards, I found they didn’t just help me. They also helped the students reflect on what they had been taught, becoming more aware of gaps in their understanding. “I didn’t realize how much I understood until I had to choose a color,” one told me. Others admitted they felt relieved when I shared the distribution of responses and they saw they weren’t alone in not fully understanding a concept.

Each batch of students has been unique. So, I am continuing to use the cards, tinkering with my material and teaching approach as I go. Although I developed this strategy for chemistry lectures, it could be used anywhere feedback matters: lab meetings, professional workshops, even research seminars. The broader lesson is that science communication, like science, thrives on evidence and awareness.

Read More