Memorizing with ADHD: Spaced Repetition and Working Memory

When I was squeezed at exam time, I sped up. The night before, I would sit down and go through a subject from start to finish, and the next morning in the exam I remembered most of it.

The problem started after the exam. If a question on the same subject came up a few days later, I felt as if I had never studied. The information had lasted until morning and then it was gone.

For a long time I thought this was about my memory being bad. The more memory research I read, the more I saw that most of the problem lay not in my memory itself but in the way I used it.

The gate and the warehouse

When talking about memorization, it helped me to separate two things.

Working memory is the temporary space that holds information in your mind right now, like holding a phone number in your head until you have dialed it. Long-term memory is the warehouse from which information can still be recalled days or years later.

In ADHD there is a strain on the gate side. A meta-analysis of working memory in children with ADHD found large differences between the groups in both verbal-auditory and visual-spatial working memory (Kasper et al., 2012). I described what this gate looks like in daily life in the article on working memory and forgetfulness.

Memorizing, on the other hand, is the work of placing information in the warehouse. When the gate is narrow, trying to push information in one go, in big heaps, gets even harder. That is exactly what last-night studying does: it piles a truckload of information at the gate in a single night.

Last-night studying does not put the information in the warehouse. It leaves it in front of the gate.

What spaced repetition says

One of the most solid findings in memory research is the spacing effect. The meta-analysis by Cepeda and colleagues brought together 317 experiments and 839 assessments from 184 articles. Spreading the same study time over time, instead of piling it into one session, produced better recall. More importantly, the best interval between repetitions grew with how long afterward the information needed to be remembered (Cepeda et al., 2006).

The same team later tested this relationship with more than 1,350 people and with delays of up to a year. Participants learned a set of facts, reviewed it after different gaps of up to 3.5 months, and were tested up to a year after the review. As the gap between repetitions grew, recall first increased and then slowly declined. The best gap was about 20 to 40 percent of the time until the test for an exam a week away, and about 5 to 10 percent of it for an exam a year away (Cepeda et al., 2008).

When I put this in my own words, it comes out like this: if I have an exam in a week, it makes sense to repeat one to three days after the first study session. For information I want to remember a year from now, I need to leave gaps of a few weeks between repetitions. In the glossary: spaced repetition.

Does self-testing work in ADHD too

What you do while repeating also matters. Looking at your notes again and pulling the information out of memory are not the same work.

There are two studies on this with students with ADHD, and both are encouraging. In the first, 25 college students with ADHD and 75 without learned one word list by studying it repeatedly in a row, and another by alternating studying with testing themselves. In the recall test two days later, both groups remembered the list they had learned by testing better, and the effect was medium-sized in both groups (Knouse et al., 2016).

In the second, 58 students with ADHD and 121 without learned key-term definitions on a computer by studying and quizzing themselves. The benefit of retrieval practice did not change with ADHD status; students with ADHD were able to regulate the practice themselves in a way similar to their peers (Knouse et al., 2020).

These two findings tell me that self-testing works in students with ADHD too. I could not find a study that tests the spacing effect itself directly in a sample with ADHD. So I assume that spaced repetition works with similar strength in ADHD, but knowing that this is an assumption.

The hard part is the calendar

In the laboratory, someone tells you when to repeat. In real life you have to remember it yourself.

Spaced repetition requires remembering to do something three days from now. This is called prospective memory, and it is one of the memory types that drops most often in ADHD. On top of that comes the difficulty of feeling time: for me the difference between "three days from now" and "two weeks from now" is often blurry. I described this in the article on time blindness.

So the good news in Knouse's studies carries over to my practice with one condition: I should not be the one remembering the timing of the repetitions. A system should.

Is memorizing a bad word

The word "memorizing" has a bit of a bad reputation among us. It carries associations such as repeating without understanding, reciting like a parrot. For a long time I too counted saying "I don't memorize, I understand" as a virtue.

Then I noticed this: understanding and remembering are not rivals. Even if I understand a concept very well, if I cannot remember its name, its definition, or which letter a formula is written with, I cannot use that understanding. Having to understand again, a few days later, something I had already understood is very familiar to me. Understanding happens once; remembering has to be rebuilt each time.

So I think of memorizing as the complement of understanding. First I understand what it is, then I leave it to spaced repetition to make it lasting.

Writing cards is also work

There is one more place where spaced repetition systems often get stuck in ADHD: preparing the cards. Ready-made decks sometimes work, but often they do not fit my own subject. Writing my own cards, on the other hand, can turn into an opportunity for procrastination in itself: making the cards pretty, coloring them, sorting them into categories.

The rule that works for me is this: one card, one single question and one short answer. Long paragraphs do not fit on a card and do not get read during review. I write the cards while studying, at that moment. The notes I say "I'll turn all of these into cards later" about most likely never become cards.

For subjects such as history, biology and geography, I wrote the subject-by-subject version of this method in the article on memorization-heavy subjects.

The small system I find worth trying

One deck, one app. A card app that does spaced repetition calculates for me which card will come on which day. Which app it is matters less than it always being the same one.

A short session each day. Ten minutes. I do not have to finish the cards; when the timer rings, I stop.

Say the answer before turning the card. Out loud, or at least inside my head, in a full sentence. Turning the card and saying "yes, I knew this" does not count as testing.

A light review the night before the exam. I do not ban the last night entirely. But instead of piling up something new that night, I go through once more the cards that have been circulating for weeks.

Seeing the same information somewhere else. When I see a term I learned on a card in a text, a video or a conversation, I mark it. When learning words in a foreign language this works especially well; I described that side in the article on learning a foreign language.

A mountain of accumulated cards. If you have not opened the app for a few days, hundreds of waiting cards can pile up, and that number can make starting seem impossible. Do not try to finish all of them in one day. Start with only twenty cards today, twenty more tomorrow. Turning accumulated cards into a punishment is the fastest way to give up on the system completely. The general form of this trap is in the article on all-or-nothing thinking.

Not turning everything into a card

Looking from the opposite direction helps too: not everything needs to be memorized. Turning a formula I look at every day, a definition I use often, or a piece of information I know where to find into a card swells the system for no reason. As the deck grows, the daily review time gets longer, and the longer it gets, the harder it is to open the app.

Before writing a card I ask myself one question: will I really need to produce this from my head, without looking anything up? If I will need it in an exam, while speaking, or when making a quick decision, it goes on a card. If I will need it in moments when I can look something up, a well-organized note is enough. Rather than trying to fill memory with every piece of information, choosing what will live in memory and what will live on paper is what keeps the deck alive.

Sometimes a person does not feel the need to learn slowly because they are able to learn fast. I still do not look down on what the last night gave me; it got me through the exam. But for the things I want to stay with me after the exam, I now know that ten minutes of boring repetition leave behind more than the excitement of the last night.