Why Students Forget and What You Can Do About It

You spend your conference period refining your lesson plan. Then the bell rings. You open the door and students begin to walk into your class. You start to teach and everything goes smoothly. You take the time to check for understanding and find that students are picking up the content. When the day is over, you head home feeling proud about what you accomplished as an educator. 

The next day, you ask students about the content from the previous lesson. Students pause and give you this confused look. You press on for answers. Some students volunteer but only remember bits and pieces. Not the whole picture. At this point, you might be telling yourself, “It’s almost like I never taught it at all.”

I understand this frustration. It can feel incredibly discouraging putting all that energy and effort into a lesson plan just for students to forget the content the next day. But what if I told you that forgetting is a normal part of learning? And that there is something we can do about it.

Why Students Forget What They Learned

The forgetting we observe in our classrooms isn’t random. It can be explained by a concept known as the Forgetting Curve.¹ Developed by psychologist Hermann Ebbinghaus in the 19th century, this theory shows that people forget a large portion of new information within the first few hours of learning it. After this initial drop, the rate of forgetting slows, but it continues gradually over time. In the end, some information is retained, but it often can’t be recalled accurately or completely.

This explains why students often only remember parts of a prior lesson. Forgetting is a natural part of how memory works. Unfortunately, it creates a real challenge for teaching because learning is cumulative and hierarchical. Students need to understand Chapter 1 to make sense of Chapter 2, and they need Chapter 2 to grasp Chapter 3. If forgetting is a natural part of the learning process, it can feel like students are being set up to fail before they even start. 

So how do we help students retain what they’ve learned so they’re prepared for what comes next?

Solving the Forgetting Problem: Review Sessions with Retrieval Practice

One way teachers can help combat forgetting is by incorporating daily review sessions in their lessons. I know. Seems pretty obvious. But bear with me.

While some teachers do begin their lessons with a review, there is a common lethal mutation that occurs when it is implemented in the classroom. Instead of asking students to recall the information, teachers often just tell students what they learned in the previous lesson.

For example, imagine you’re teaching students how to determine the number of protons, neutrons, and electrons using the Periodic Table. In the previous lesson, you covered the history of the atomic model and introduced the characteristics of protons, neutrons, and electrons.

To review, a teacher might say, “Okay class, remember yesterday when we went over the subatomic particles? Protons are positive and located in the nucleus. Neutrons have no charge and are also in the nucleus. Electrons are negative and found outside the nucleus in the electron shell.”

In this scenario, the teacher is telling the students what they previously learned. Even though the content is being reviewed, the students aren’t processing the information deeply because they are not being asked to recall the information.

For a more effective review, teachers should ask students to recall the information instead²: “On a blank sheet of paper, I want you to write the characteristics of the following subatomic particles: proton, neutron, and electron. Try to do this without looking at your notes or consulting with a partner. We will do that later.”

This approach allows students to actively engage with the material by engaging in recall. Recall occurs when students attempt to retrieve the information from their long-term memory. Recall is important because it strengthens memory and deepens understanding.³ Answering review questions without using notes requires significant mental effort, which helps strengthen neural networks and make learning stick. This effortful practice is key to long-term retention. In addition, recalling previously learned material prepares students to better understand and connect new concepts. This process is known as retrieval practice.

How to Design Effective Questions for Review Sessions

Incorporating retrieval practice into your review session is essential, but it’s equally important to be intentional with the questions you ask. The right questions should focus on the knowledge students need to recall in order to be successful in the day’s lesson.

Start by asking yourself, “What do students need to remember from previous lessons in order to understand today’s learning objective?”

Let’s return to the earlier example. The teacher says, “On a blank sheet of paper, write down the characteristics of a proton, neutron, and electron.” Notice that the teacher didn’t ask students to recall the entire history of the atomic model, despite this being covered in a previous lesson. That’s because the day’s lesson objective was to determine the number of protons, neutrons, and electrons using the Periodic Table. Reviewing the characteristics of protons, neutrons, and electrons was a purposeful choice. It directly supports the new learning. The history of the atomic model? It can but not so much.

Incorporating Retrieval, Interleaving, and Spaced Practice in Daily Review Sessions

Sometimes teachers push back, saying this approach leaves out other important concepts that were previously covered. I remind them that a review session doesn’t need to cover everything students have learned in the past. It should only focus on prior content that is most relevant to the current lesson. The other concepts can be revisited when they’re relevant. For example, students don’t necessarily need to revisit the history of the atomic model to determine the number of protons, neutrons, and electrons using the Periodic Table. However, when they start drawing atomic structures, that history becomes important because the Bohr model is often used to draw these diagrams and is part of the development of the atomic model. Therefore, when covering drawing atomic structures, that will be the perfect time to revisit the history of the atomic model.

In addition, this approach allows us to take advantage of interleaving and spaced practice.

Interleaving is a learning strategy that involves mixing up different topics or types of problems during practice, rather than focusing on just one concept at a time.⁴ When you ask students questions about topics covered in prior lessons, you are naturally engaging them in interleaved practice. For example, if today’s lesson focuses on using the Periodic Table to determine the number of protons, neutrons, and electrons, you might include review questions that touch on related ideas like the characteristics of protons, neutrons, and electrons. These questions come from different lessons, but they’re conceptually connected. Students must think critically about how each idea differs and when it applies. This comparison helps solidify their understanding and allows them to better recognize which strategy or concept to use in a new situation.

Spaced practice is a learning strategy that involves reviewing information over multiple sessions, spaced out over time, rather than cramming it all at once.⁵ When you revisit topics from previous lessons during daily review, you are naturally engaging students in spaced practice. For example, you might not review the history of the atomic model every week. But when the class begins learning about drawing atomic structures, that’s the perfect time to bring it back. Even if students find it hard to recall something they haven’t seen in a while, that mental effort actually makes the memory stronger. Each time students retrieve the information after some forgetting has occurred, their retention improves. Spaced practice helps move knowledge from short-term to long-term memory, making it more likely students will remember and apply it in the future.

How Much Time Should You Spend on Review Sessions?

Review sessions should be brief and focused. Ideally, a review should be done at the beginning of a lesson and take around 5-10 minutes. If you spend too much time revisiting old content, you risk falling behind on the curriculum. Overextended reviews can also slow the pace of the lesson, which may cause students to lose focus and disengage. That’s why your review should target only the important information students need from the previous lesson to successfully engage with the current learning objective.

Honorable Mentions

This blog post was inspired by TEACH Fast: Focused Adaptable Structured Teaching by Dr. Gene Tavernetti. If you’re looking to bring more evidence-informed strategies into your classroom, I highly recommend this book. It’s one of the few that clearly connects cognitive science to lesson design, with strategies grounded not just in research, but in real classroom experience.⁶

Notes:

1. Ebbinghaus, H. (2011). Memory: A contribution to experimental psychology (H. A. Ruger & C. E. Bussenius, Trans.). Martino Fine Books. (Original work published 1885) ↩︎
2. Barideaux, K. J. (2025). Enhancing Final Exam Performance Through Retrieval Practice: Evidence From a Diverse College Sample. Teaching of Psychology, 0(0). https://doi.org/10.1177/00986283251352475 ↩︎
3. Roediger, H. L., & Butler, A. C. (2011). The critical role of retrieval practice in long-term retention. Trends in Cognitive Sciences, 15(1), 20-27. https://doi.org/10.1016/j.tics.2010.09.003 ↩︎
4. Taylor, K., & Rohrer, D. (2010). The effects of interleaved practice. Applied Cognitive Psychology, 24(6), 837-848.  https://doi.org/10.1002/acp.1598 ↩︎
5. Bjork, R. A., & Bjork, E. L. (2011). Making things hard on yourself, but in a good way: Creating desirable difficulties to enhance learning. In M. A. Gernsbacher, R. W. Pew, L. M. Hough, & J. R. Pomerantz (Eds.), Psychology and the real world: Essays illustrating fundamental contributions to society (pp. 56-64). Worth Publishers. ↩︎
6. This is not a paid sponsorship. I genuinely find this book valuable. ↩︎