How to write flashcards that teach, and how to study them

A flashcard teaches when its front is a question you must answer from memory and its back is one short, checkable answer. One idea per card, no answer visible on the front, a question rather than a keyword, and a reason or an example on the back where there is one. Study the cards by attempting before you flip, marking yourself honestly, and bringing each card back on a growing gap. Most "flashcards" fail the first rule. This page is the rules for writing a card, the card types, a real idea rewritten into six cards, and the routine for studying them.

Why most flashcards fail

Open a typical deck and the first card reads "Chain rule" on the front. The back is a paragraph. That card cannot be answered, only recognised: you turn it over, read the paragraph, nod, and move on. Nothing was retrieved, so nothing was strengthened. Flashcards are a container for recall and spacing, and a container with a keyword on the front holds neither.

The other common failures look different and are the same fault:

• Ten facts on one card. The front says "The French Revolution" and the back is a timeline. You will know some of the back and not the rest, and the card cannot tell you which.
• The copied definition. The back is the textbook's sentence, word for word. You learn the sentence's rhythm rather than the idea, and a question asked in other words misses it.
• The card you recognise but could not produce. You have seen the back twenty times. Asked the question in class, you cannot say it. Familiarity and recall are different things, and the card only ever tested the first.

Every one of these is fixed in the writing, before any studying happens. The learning comes from the retrieval, and the card's job is to force one (Roediger and Karpicke 2006). A card that does not force a retrieval is a very small page to reread.

The rules for writing a card that teaches

Making flashcards is a writing task with seven rules. Several of them come from Piotr Wozniak's "Twenty rules of formulating knowledge" (1999), the best-known list of its kind, and the rest follow from the research on retrieval.

1. One idea per card. Wozniak calls this the minimum information principle. If a card has two things to know, split it. Small cards are answered fast, marked honestly, and scheduled separately, so the half you know does not drag the half you do not.
2. A question on the front, phrased as a teacher would ask it. Not "Osmosis" but "Which way does water move across a membrane in osmosis, and why?" If you can imagine the front being read aloud in an exam, it is a question.
3. Nothing on the front that gives the answer away. A front that reads "Define osmosis: the movement of water across…" tests nothing. The front asks; the back answers; the two do not overlap.
4. A back short enough to check in two seconds. One line, two at most. If the answer needs a paragraph, the card holds more than one idea, and rule 1 applies.
5. The why, or an example, on the back. A fact with its reason is remembered longer than the bare fact, and an example tells you what the fact looks like in a question. Keep it to one more line.
6. Your own words. Write the back as you would explain it to a friend. The textbook's wording goes on the card only when the exact wording is what is tested, such as a law or a definition the course marks on.
7. A list becomes one card per item, plus one card for the order or the count. For the four stages of mitosis: four cards, each "What happens in prophase?" and so on, and one card "Name the four stages of mitosis in order." The list card alone would be answered in pieces and marked by feel.

A card that passes all seven is small, sharp and a little dull to look at. That is the right look.

Card types: basic, reversed, cloze

Three shapes cover almost everything.

Basic. A question on the front, an answer on the back. "What is the derivative of sin x?" → "cos x". The default for a fact, a formula or a one-step reason.

Reversed. The same pair written in both directions, as two cards. "What is the term for a reaction that releases heat?" → "exothermic", and "What does exothermic mean?" → "it releases heat to the surroundings". Use reversed cards for vocabulary and definitions where the exam might ask either direction. Vocabulary flashcards for a language are the classic case: word to meaning and meaning to word are two different retrievals, and knowing one does not give you the other.

Cloze. A sentence with one gap. "The derivative of sin x is ___." → "cos x". Cloze cards are quick to write from a sentence in your notes and they keep the context around the gap, which helps when the fact only makes sense in a sentence. Wozniak's rules lean on them heavily. The limit is the gaps: one is best, two or three at most, and never a sentence where every noun is a blank, because then the front is a puzzle and not a question.

Pick the shape by the material. A formula wants a basic or a cloze card. A term wants a reversed pair. A process wants one basic card per step and a list card for the order.

When a card should become a worked problem instead

Math flashcards have a limit, and it is worth knowing where it is. A card can hold a fact: a formula, a definition, the sign of a derivative. It cannot hold a procedure. "Solve a quadratic by completing the square" is not an answer you can check in two seconds, and a card that tries to hold the whole method becomes a paragraph you reread.

So for a procedure, the card changes shape. The front is a problem: "Solve x² + 6x + 2 = 0 by completing the square." The back is the first line of the method and the final answer: "Move the constant, add (6/2)² = 9 to both sides; x = −3 ± √7." You study it by redoing the whole problem on paper, then checking the first line and the answer. The card is a prompt to redo a solved problem cold; the paper is where the learning happens.

The wrong line, when you make one, does not go on the card. It goes in an error log beside the right line: "completing the square: half the coefficient, then square it." The card stays a clean problem, the log holds your mistakes, and the next time the card comes up you read the log entry first.

Worked example: one idea, rewritten into cards

Take one idea from Grade 12 advanced functions (MHF4U): the laws of logarithms, idea 11 on the MHF4U course map. Here is the card most students write for it.

Front: "Log laws." Back: the three laws and two examples. Six lines. It breaks rules 1, 2, 4 and 5 at once, and it can only be read, never answered.

The same idea, rewritten as six cards:

#	Type	Front	Back
1	Cloze	log(ab) = ___	log a + log b
2	Basic	What is log(a/b) in terms of log a and log b?	log a − log b
3	Basic	Rewrite log(aⁿ) without an exponent.	n log a
4	Reversed	Which law turns a sum of logs into one log?	The product law: log a + log b = log(ab)
5	Problem	Condense 2 log 5 + log 4 (base 10).	2 log 5 = log 25; log 25 + log 4 = log 100 = 2
6	Basic	Why does log(ab) = log a + log b? One line.	Because bˣ · bʸ = bˣ⁺ʸ, and a log is an exponent

Check card 5 yourself before you trust it. The power law turns 2 log 5 into log 5², which is log 25. The product law turns log 25 + log 4 into log(25 × 4) = log 100. In base 10, log 100 = 2 because 10² = 100. The answer is 2.

Notice what the six cards do that the one card could not. Card 1 and card 4 are the same law from two sides, so you learn to recognise it in a question going either way. Card 5 makes you use two laws together, which is how the exam asks. Card 6 is the why, and it is the card that stops you from inventing a law that does not exist, such as log(a + b) = log a + log b. Six small retrievals, each marked on its own, instead of one paragraph nodded at.

How to study the cards

Writing the cards is half the work. The other half is a routine, and the routine has four parts.

Attempt before you flip, always. Say the answer aloud or write it down before you turn the card. "Yeah, I know this one" is not an attempt. The attempt is the retrieval, and the retrieval is the learning; everything in the active recall guide applies to a card as it applies to a blank page. A card you flipped first counts as rereading for the day, and you should mark it so.

Mark on three levels. Right: the answer came, complete, without a pause. Struggled: you got there slowly, in pieces, or were not sure until you checked. Wrong: anything else, including "I basically had it." Write the mark down; the pile is the schedule.

Bring each card back on a growing gap. Right cards move out: one day, then three, then seven, then fourteen. Struggled cards keep their current gap. Wrong cards come back tomorrow. On paper this is a Leitner box, five sections with the cards moving forward on a Right and back to the first on a Wrong; the full method is in the spaced repetition guide, and chapter 2 of the free playbook is the same schedule on one page. Flashcards and spaced repetition belong together because the growing gap is what makes the deck last to the exam rather than to tomorrow (Cepeda et al. 2006).

Shuffle the deck and mix units. Studying the log-law cards as a block of six means the heading answers for you: you know every card is a log law before you read it. Mixed into a deck with trig and rational-function cards, each card has to be recognised before it can be answered, which is the harder and more useful retrieval. Why mixing beats blocked practice has the research; for a deck, the practice is simply to shuffle.

The spacing point is not a small one, and students get it backwards. Kornell (2009) had learners study word pairs either as one large stack, so each card came back after a long gap, or as four small stacks studied one after another, so each card came back quickly. Spacing beat massing for about 90 per cent of the learners. Asked afterwards which had worked better, 72 per cent said the massed stacks had. The small stacks felt better because each card was fresh when it came round, and that feeling was wrong. If a big shuffled deck feels harder than a small one, that is the method working.

The cards that waste time

• Pretty cards. Colour-coding, hand lettering, a border. The decoration is pleasant and it is not the learning. An hour on the look of the cards is an hour not spent answering them.
• Cards from someone else's set, without reading the source. You cannot check them. If a card is wrong or out of date, you will learn the wrong thing with full confidence, and you have no way of knowing which card it is. Write your own, or at least read each borrowed card against your notes before it enters the deck.
• Cards for things you already know. They pad the deck, pad the streak, and spend the review time on retrievals that teach nothing. If a card has been Right three times in a row with no pause, retire it.
• Cards with the answer visible on the front. Rule 3 again, because it is the most common break.
• A deck of 400 you never return to. A deck is a schedule, not a trophy. Forty cards reviewed on the right days beat four hundred written the night before and read once.

Paper, digital, or an app?

Paper index cards work. They force a short answer, because the card is small; they need no screen, so nothing else is on the desk; and a Leitner box of five rubber-banded piles is a complete schedule. Printable flashcards, a grid of blanks you cut up, are the same thing for less than the price of a pack of cards.

Digital flashcards and online flashcards add two things paper cannot: the schedule is computed for you, card by card, from your marks, and a card can carry a diagram or a photo of a graph. A flashcard app also keeps the deck on your phone, which means the ten minutes on the bus are review time. The cost is the screen, and the risk is that the deck becomes something you tend rather than something you answer.

A flashcard maker that generates cards from your notes or a recording saves the writing time and brings a new risk: a generated card can break every rule above and look fine. Read each one against the seven rules before it enters the deck, and delete freely. What a flashcard maker should do to your cards goes through what to check.

Whatever you use, the medium does not decide the result. The rules for writing the card and the habit of attempting before you flip do. The review that rated ten common study techniques put practice testing at the top (Dunlosky et al. 2013), and a flashcard is a practice test exactly as far as its front forces an answer.

The method on one page

Writing a card:

1. One idea per card.
2. A question on the front, as a teacher would ask it.
3. Nothing on the front that gives the answer away.
4. A back you can check in two seconds.
5. The why, or an example, on the back.
6. Your own words.
7. A list becomes one card per item, plus one card for the order.

Studying the deck:

• Attempt before you flip, aloud or in writing.
• Mark Right, Struggled or Wrong, and write it down.
• Right moves out (1, 3, 7, 14 days); Wrong comes back tomorrow.
• Shuffle, and mix units.
• Retire cards that are Right three times running; add cards after each class.