Spaced Repetition vs Interleaving: What Each One Does
The short version of spaced repetition vs interleaving: spacing is about time (review the same topic again after a gap of days), and interleaving is about order (mix different topics or problem types inside one session instead of doing one at a time). They solve different problems, so the best study plans use both.
If you want the spacing half done for you, FlashDeck turns your notes into cards and shows only the ones due each day: Build my study plan.
What spacing means (what is spaced repetition?)
So... what is spaced repetition, and how do you practice it? It's reviewing the same material several times, with gaps between reviews that get longer each time you remember it.
A typical pattern:
- Learn it today.
- Review tomorrow.
- If you remembered, review again in 3 days.
- Then in a week.
- Then in a few weeks.
If you forget at any step, the gap goes back to a day.
The problem spacing solves: forgetting. Without spacing, you learn a topic, move on, and it quietly fades until the final. Spacing brings it back just as it starts to slip, which makes the memory stronger each time.
What it feels like: slightly annoying. You'll forget some cards and have to dig. That's the point.
What interleaving means
What is interleaving? It's mixing different kinds of problems or topics within one practice session. The opposite is blocked practice: twenty problems of type A, then twenty of type B.
Blocked practice: A A A A A B B B B B C C C C C Interleaved practice: A C B B A C A B C A
The problem interleaving solves: choosing. On a real test, questions don't come labeled "this one is from Chapter 4." Blocked practice lets you skip the step of figuring out which method to use, because you already know. Interleaving forces you to decide every time.
What the research says: In a math study by Rohrer and Taylor (2007), students who practiced mixed problem types did better on a test a week later than those who practiced in blocks, even though the mixed practice felt harder at the time. In another study, Kornell and Bjork (2008) found people got better at recognizing painters' styles when paintings by different artists were mixed together, and most of them wrongly believed blocking had worked better.
What it feels like: messy and slow. You'll get more wrong during practice. That's normal.
When each helps most (interleaving vs spaced repetition)
| Spaced repetition | Interleaving | |
|---|---|---|
| Changes | When you review | The order within a session |
| Fixes | Forgetting over days and weeks | Mixing up which method or idea applies |
| Best for | Facts, definitions, formulas, vocab, dates | Problem solving, telling similar things apart |
| Needs | Several sessions over time | Several topics you've already learned |
| Main tool | Flashcards on a schedule | Mixed practice sets |
| Feels like | Forgetting some cards | Getting more wrong while practicing |
A simple rule:
- If you're forgetting things, you need more spacing.
- If you know the material but freeze on which method to use, you need more interleaving.
One catch with interleaving: it works best after you've learned the basics of each topic. Mixing three types of problems you've never seen before is just confusing. Learn in blocks first, then mix.
How to use both in one week
Here's a one-week plan that combines active recall, spaced repetition and interleaved study. It works for most classes.
Daily (about 10 minutes): spaced cards
- Review only the flashcards that are due today.
- Answer each one before flipping (that's the active recall part; more in spaced repetition vs active recall).
- Knew it: it waits longer. Missed it: it's back tomorrow.
Twice a week (20–30 minutes): an interleaved practice set
- Pull questions from at least three topics: this week's, last week's and something from earlier.
- Shuffle them. No headings.
- For each question, first write down which topic or method it needs, then solve it.
Once a week (5 minutes): feed the deck
- Any mistake from the mixed set becomes a new card. Make it about the moment you got confused, like "How do I tell a t-test question from a chi-square question?"
The daily step is the one that breaks down fastest on your own. Tracking which of 200 cards is due today, and which ones you missed yesterday, is real work. FlashDeck does it. Paste your notes or upload slides as a PDF, and it writes one card per fact, definition or formula from only what you gave it, then shows just the cards that are due each day. Build my study plan
Examples for math, science and languages
Interleaving for math
- Spacing: cards for formulas and "what's the first step?" decisions. See does spaced repetition work for math for sample cards.
- Interleaving: a mixed set of derivatives using the product rule, quotient rule and chain rule, unlabeled. The skill is picking the rule.
Science (biology, chemistry, psychology)
- Spacing: cards for vocabulary, processes and key experiments. "What happens in the light-dependent reactions?"
- Interleaving: mixed questions across units. For AP Psych, alternate between classical conditioning, operant conditioning and observational learning examples and name which one each scenario shows.
Languages
- Spacing: vocab and grammar rule cards, reviewed on a schedule.
- Interleaving: a mixed drill of verb tenses (present, past, future) instead of a page of only past tense. You have to pick the tense from context, just like in a real conversation.
History
- Spacing: cards for dates, people and causes.
- Interleaving: mixed short-answer prompts from different eras. "Which period does this document come from, and why?"
Start with the half that's easiest to automate
You now know the difference between spaced repetition and interleaving. Spacing is the half that needs a daily schedule, and FlashDeck handles that: paste one unit of notes, delete any cards you don't need, and your first due list is ready in about a minute. Then add a mixed practice set twice a week and you're using both.
FAQ
Is interleaving the same as spaced repetition?
No. Spaced repetition spreads reviews of the same material across days. Interleaving mixes different topics in one session. They often happen together, because mixing in older topics also spaces them out, but they're different ideas.
What is spaced repetition learning in one sentence?
It's reviewing material at growing time gaps, so you practice remembering it right before you'd forget, which makes it last longer.
What are some good interleaving examples for students?
Mixing different types of math problems in one set, alternating between verb tenses in a language drill, or answering shuffled questions from several units of a science course instead of one chapter at a time.
Should I use interleaving vs spaced repetition for a test next week?
Use both. Do daily spaced flashcards for the facts and formulas, and a couple of mixed practice sets for problem solving. If you only have time for one, pick the one that matches your weak spot: forgetting (spacing) or mixing up methods (interleaving).
How do you do spaced repetition without an app?
Use paper flashcards sorted into boxes (review box 1 daily, box 2 every few days, and so on) or a spreadsheet with a next-review date. It works; it just takes more tracking.