What do we remember? What do we forget? And why?

The reasons our minds hang on to some pieces of information, but let go of others, can seem mysterious. It doesn't appear to be a process under our control—otherwise we wouldn't remember a commercial jingle we heard ten years ago, and we wouldrecall that important fact that . . . wait, what was it?

Memory operates by its own rules, and once we understand them, we can exert a lot more control over what we remember. One of these rules is explored by Dan Willingham, a cognitive scientist at the University of Virginia, in a recent article in The Atlantic magazine.

The thing that makes memories of what we’ve learned “indelible,” Dan writes, is returning to that material again and again:

“[The] invisible residue of old memories helps a person remember that same material again more quickly than before. Clever research studies on this phenomenon tested Mormon missionaries who learned a foreign language but didn’t use it again for decades; forgotten vocabulary was quickly relearned. Other research in more controlled laboratory situations showed comparable results.”

Repeatedly revisiting material doesn’t mean we’re stuck doing the same thing over and over again. In many subjects, like math, we constantly return to basic skills and knowledge we learned earlier in the process of working on newer, more advanced material. Dan continues:

“In one rather remarkable study, researchers administered an algebra test among adults who had taken algebra anywhere from months to decades previously. Most of the adults struggled to remember how to do the equations, but those who’d studied math beyond calculus (subjects whose mastery requires an understanding of algebra) could still work basic algebra problems—even if they had not done so for decades. In other words, several years of practicing algebra in more advanced math courses made the former stick permanently.”

What implication can we draw from such research? Dan concludes:

“When thinking about what we expect students to learn, it’s not enough that content be ‘covered.’ Evidence suggests that a student must use such content in his or her thinking over several years in order to remember it for a lifetime.” [Italics mine.]

I think there’s another implication we can draw, one with a shorter time frame than “several years.” When we’re working with a briefer period—say, an academic semester—we can think in terms of  what researchers Katherine Rawson and John Dunlosky have called “successive relearning.”

The best way to learn and remember, they write, is to combine retrieval with spacing. That is: test yourself on the material you need to learn, then wait a few days, and test yourself again. In the interval your memory of the material will have faded a bit, but by successively relearning it, you will cement it in your memory.

This research clearly stands as an argument against the infrequent, high-stakes testing regime that prevails in many schools, and an argument in favor of frequent, low-stakes testing, with testing episodes spread out over time (and with old and new material interleaved for good measure).

In the e-course I launched earlier this week, Turn Testing Into Learning, I provide step-by-step instructions for implementing retrieval, spacing, and interleaving. Using these techniques, you can take control of what you remember. It's not hard once you know how.

You can try out a sample lesson by clicking here.