I've noticed that a few weeks after the end of a semester, most students can't remember the majority of their courses' content. Even the students that did well on the final exam usually have trouble recalling much of the curriculum after the semester has ended.

In most high school classes, students learn the units one at a time, have a test after each unit, and take a final exam at the end of the semester. I think that this type of structure makes it more likely for students to forget what they've learned in the future, and a certain change in this framework could help students remember more after they've finished their classes.

Psychologists have modeled our forgetting patterns with a "forgetting curve," a graph that represents this effect. This curve approximates the retention of material at different times after learning the material. The forgetting curve looks like this:

The graph is pretty intuitive; repeating material leads to higher retention rates. This is why cramming works in the short term, but doesn't lead to long term memory.

The thing is that the high school class structure doesn't really encourage this necessary repetition. Each unit is only learned twice: once when the students first learn it, and once before the final. Retention that follows this learning pattern doesn't usually last for weeks or months after the final.

To counteract the forgetting curve, I think that school curriculums should make use of spaced repetition, a studying technique that interrupts the forgetting curve by learning in spaced-out intervals. A student using spaced repetition would review their units several different times before a test, effectively having the material in their long term memory when tested. In fact, spaced repetition is so powerful that using spaced repetition in a single study session is more effective. A study in 2011 tested spaced repetition by having participants try to remember words in Swahili. They divided the participants into the four following groups:

Group 1: Studied each word once

Group 2: Studied each word once and recalled each word once

Group 3: Studied each word once and recalled each word many times directly after studying it

Group 4: Studied each word once and spaced out an equal number of recall tests as Group 3

Here were their results:

You can see that Group 4 did the exact same amount of work as Group 3, but because they spaced out their studying, their results were 50% better. This simple change yielded significantly more results while requiring little extra effort. Spaced repetition can also be applied outside the world of academics; it’s effective in learning most skills. Many musicians can relate to having better results after practicing in several distinct sessions- this is spaced repetition in action. If you're interested in a more in-depth discussion of spaced repetition, here's a video by productivity guru Ali Abdaal.

I think that having cumulative tests is one of the easiest ways to implement spaced repetition in a school curriculum.  For example, the Unit 5 test could have 1-2 reasonably in-depth questions from Units 1-4, and have the rest of the questions from Unit 5. This would force students to review previous units at regular intervals, making them more likely to succeed on the final and remember the material for a longer time. Students wouldn’t even need to spend much time studying for the final, since they already would have the majority of the material in their long-term memory. Another solution is to have one or more midterms, which would lead to more repetition and later retention.

In my experience, students usually lack the motivation to do extra studying without an incentive; when school went online last spring, many student's commitment to academics dropped. It's therefore unlikely that most students would implement spaced repetition independently throughout the semester, so I think creating a course structure around spaced repetition would lead to stronger results than only advising extra revision.

I encourage you to try using spaced repetition the next time you're learning something new. You won't be disappointed.