To study several subjects at once without forgetting them, rotate them instead of finishing one before the next. Give two or three subjects a short block each day, open every block with a quick recall quiz on that subject's last session, mix problem types inside each subject, and do one mixed review a week.
Interleaving is a study method where you mix different types of problems or concepts in one session instead of practicing one type at a time. In a 2015 study in the Journal of Educational Psychology, Rohrer, Dedrick and Stershic gave seventh graders the same math problems, with some problem types practiced mixed and others blocked. Thirty days later, students scored 74 percent on the problems they had practiced mixed and 42 percent on the ones they had practiced blocked.
Quick Answer: Rotate Subjects, Mix Problems, Test First
Juggling subjects is not the problem. Leaving a subject alone too long, and practicing it in a way that feels easy, is. Rotate two or three subjects a day so each one comes back after a short gap. Inside each subject, mix problem types. Start every block by recalling what you did last time before you learn anything new.
The question came from a student on r/GetStudying who asked how to study several subjects at once without losing retention on all of them. The fix is mostly about scheduling. The rest of this post explains why the rotation works, where the research is weaker than people claim, and how to plan a week.
Why studying several subjects at once makes you forget
You forget a subject while you are away from it, and you notice too late because the last session felt good. Two things cause this. Long gaps let a subject fade before its next turn. And practicing one kind of problem at a time feels smooth, so you think it stuck when it did not.
The first cause is simple. If you study biology on Monday and next open it on Friday, four days of forgetting happen in between. With more subjects, the gaps get longer unless you plan for them, and most people study whatever has the nearest deadline.
The second cause is sneakier. When you do a set of problems that are all the same type, each one gets easier. You already know which method to use, because it was the method for the last problem. That smooth feeling reads as learning, but it is mostly momentum.
A 2008 study by Kornell and Bjork in Psychological Science, "Learning Concepts and Categories: Is Spacing the 'Enemy of Induction'?", measured this trap directly. People studied paintings by several artists, either one artist at a time (blocked) or mixed together (interleaved). Then they had to name the artist of new paintings they had never seen. In Experiment 1a, people named the right artist 61 percent of the time for artists they had studied interleaved, and 35 percent for artists they had studied blocked. 78 percent of participants did better with interleaving. Yet 78 percent said blocking was as good as or better than interleaving.
You cannot trust the feeling at the end of a session. You need a schedule that brings each subject back, and a quick test that shows you what stayed.
Spacing vs interleaving: the honest distinction
These are two different ideas that often get mixed up. Spacing means coming back to the same material after a gap. Interleaving means mixing similar types of problems or concepts in one session. Rotating unrelated subjects mostly gives you spacing. The strongest interleaving results come from mixing confusable things inside one subject.
Many study guides say "switch subjects often, it is called interleaving, and the research says it works". That is only half right. When you go from history to chemistry, there is little chance of confusing the two. The benefit of interleaving comes from making you tell apart things that look alike, and history and chemistry do not look alike.
The biggest review of the topic is clear about this. A 2019 meta-analysis by Brunmair and Richter in Psychological Bulletin, "Similarity matters", pooled 59 studies and 238 effect sizes. The overall interleaving effect was moderate (Hedges' g = 0.42). It was strongest for paintings (g = 0.67) and other visual material, and small for math tasks (g = 0.34). For expository texts, the kind of reading you do in most courses, the result was unclear and not significant. For word learning, blocking actually won (g = -0.39). The authors' conclusion is in the title: interleaving helps most when the categories are similar to each other and easy to confuse.
So what does juggling several subjects really buy you? Spacing. Each subject gets revisited after a gap, and spacing has strong support. A 2006 meta-analysis by Cepeda, Pashler, Vul, Wixted and Rohrer in Psychological Bulletin, "Distributed practice in verbal recall tasks", covered 839 assessments in 317 experiments from 184 articles. One of its findings is that the best gap between study sessions grows as the time until the test grows. A test next week wants shorter gaps. A final exam months away can use longer ones.
A 2013 review by Dunlosky and colleagues in Psychological Science in the Public Interest rated 10 common learning techniques. Practice testing and distributed practice got high utility ratings, interleaved practice a moderate one, and rereading and highlighting low ones.
The practical rule that follows from all this has three parts. Rotate subjects to get spacing. Interleave problem types inside each subject to get the interleaving effect. Test yourself at the start of each block so you see what spacing let slip. If you want more on the spacing side, our guide to how spaced repetition boosts learning goes deeper.
Your realistic options, compared
There are a handful of realistic ways to handle several subjects, and most cost nothing. They differ in how much spacing they build in, whether they train you to pick the right method, and what they are weak at. The table lays them out honestly so you can combine the two or three that fit how you study.
| Option | Cost | What it does well | Weak spot | Best for |
|---|---|---|---|---|
| One subject per day (day blocking) | Free | Long, focused sessions on one subject | Each subject waits days for its next turn, and long blocks of one topic feel fluent without testing you | Big projects that need several hours of unbroken focus |
| Daily time blocks per subject (2-3 subjects a day) | Free | Built-in spacing, since every subject comes back after a short gap | Needs a schedule you actually keep | Anyone juggling several courses or exams at once |
| Interleaved problem sets within a subject | Free | Trains you to pick the right method for each problem | Feels harder, and your scores during practice are lower | Math, science, and any subject with similar problem types |
| Anki flashcards | Desktop app, AnkiWeb sync and AnkiDroid for Android are free; AnkiMobile for iOS is a paid app | Strong spaced review of facts, terms and formulas | Weak for problem-solving skills; making good cards takes time | Vocabulary, definitions and facts you must keep for months |
| LearnPath | Free plan: 2 paths in total, step 1 of each; later steps, unlimited paths and unlimited quizzes are Pro | Builds a path of YouTube lessons in order for a topic, with a quiz after each lesson and review cards (Free shows 5 review cards at a time) | Free covers only the first step of each path, and it runs on YouTube lessons, so it suits topics taught well on YouTube | Learning a new topic from video in a set order |
A few honest notes. The first two rows are the real choice for most people, and the second wins for retention. Day blocking is not wrong, it just stretches the gaps. The third row is the one people skip because it feels worse. That is the Kornell and Bjork trap again: lower scores during mixed practice are normal.
Anki and LearnPath are tools, not methods. Anki handles spaced review of facts very well and does little for problem-solving. LearnPath gives you an ordered set of lessons with a quiz after each one, which helps when a subject is a new topic you are learning from YouTube. Neither one decides your weekly rotation for you.
A weekly plan for studying several subjects
The plan below puts the research into a routine you can start this week. It uses short daily blocks per subject for spacing, a recall quiz at the start of each block, mixed problem types inside each subject, and one mixed review at the end of the week. Adjust the block lengths, keep the structure.
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List your subjects and pick two or three per day. Write every subject down. Assign two or three to each day so that every subject comes up at least every few days. Subjects with an exam soon get more slots. This is the spacing part, and the schedule matters more than the exact times.
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Give each subject a 30 to 60 minute block. That is long enough to get real work done and short enough to fit two or three subjects in one day. Put a short break between blocks. If a block keeps running over, our post on what to do when topics take longer than planned covers how to fix your estimates.
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Open every block with a 5-minute recall quiz. Before you look at anything, write down what you remember from that subject's last session. Key ideas, a formula, a worked problem from memory. Then check your notes. This is practice testing, one of the two techniques the Dunlosky review rated high. It also shows you exactly what faded while you were away.
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Mix problem types inside the subject. Once you have reviewed, practice with a mixed set. In math, combine problems from the last few sections instead of doing twenty of the newest kind. In a science, mix questions about concepts that are easy to confuse. This is where the interleaving research is strongest, so put your mixing here.
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Learn the new material last. After the quiz and the mixed practice, move on to new content. End the block by writing two or three questions about what you just learned. Those become the start of next session's recall quiz.
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Do one mixed review a week. Pick one session at the end of the week. Pull questions from every subject, shuffle them, and answer from memory. Mark what you missed and give those topics extra time next week. This catches the subjects that slipped through the rotation.
A sample day might be chemistry in the morning, history after lunch, and a short math block in the evening. The order matters less than making sure no subject goes quiet for long.
How to do this when your subjects are YouTube courses
Learning from YouTube playlists makes rotation easy to break, because the next video plays automatically and one playlist can eat a whole evening. Treat each playlist as one subject in your rotation. Watch one or two lessons per block, pause, test yourself from memory, then stop and switch to the next subject.
The pull of a playlist is the same as day blocking. One more video feels like progress, so you watch five lessons of one course and none of the others. Set a stopping point before you press play.
Video also makes rereading's twin, rewatching, very tempting. If you did not catch something, it is easy to scrub back and watch it again. Rewatching feels like review but works like rereading. We compare the two approaches in active recall vs rereading notes. The better move is to close the video and write what you remember, then rewatch only the part you could not explain.
Three habits help with playlists in particular:
- Write down where you stopped. Note the lesson and the time so the next block starts without hunting.
- Keep one question list per subject. After each lesson, write two or three questions from it. Use them for the next block's opening quiz.
- Mix lessons for the weekly review. Pull questions from several playlists in one session, so you have to switch between them.
If you use LearnPath for one of your subjects, the quiz after each lesson can serve as the test step inside that block. You still need to put that subject on your rotation next to the others. A tool that orders lessons for one topic does not plan your week.
Common mistakes when juggling several subjects
Most retention problems with several subjects come from a few habits. They feel productive in the moment, which is why they stick. Knowing them makes it easier to catch yourself. The fix for almost all of them is the same: shorter gaps, more mixing inside a subject, and a quick self-test before anything new.
- Studying only whatever is due next. Deadlines pull all your time into one subject. The others go quiet and fade. Keep every subject on the rotation, even if its slot is short this week.
- Calling subject-switching "interleaving" and stopping there. Switching subjects gives you spacing, which is good. The interleaving benefit comes from mixing similar problems inside a subject. Do both.
- Trusting the feeling at the end of a block. A smooth, blocked session feels like learning. Kornell and Bjork showed that most people misjudge this. Test yourself at the start of the next session instead.
- Rereading or rewatching as review. The Dunlosky review rated rereading low. Close the material and recall first.
- Dropping the weekly mixed review. It is the one session where all your subjects meet. Without it, small gaps add up unnoticed.
Frequently Asked Questions
These are the questions people ask next, each answered so it makes sense on its own. The short version of all six: rotate subjects for spacing, mix problem types inside each subject, and test yourself at the start of every block.
How do you study multiple subjects at once without forgetting them?
Rotate them instead of finishing one before starting the next. Give two or three subjects a short block each day, start every block with a quick recall quiz on that subject's last session, and mix problem types inside each subject. The rotation spaces out your practice, and the opening quiz shows you what is fading before it is gone.
What is interleaving in studying?
Interleaving is a study method where you mix different types of problems or concepts in one session instead of practicing one type at a time. In a 2015 study by Rohrer, Dedrick and Stershic, seventh graders scored 74 percent on a test 30 days later on math problems they had practiced mixed, versus 42 percent on problems practiced in blocks.
Does switching between different subjects count as interleaving?
Not really. The research on interleaving is strongest when you mix similar, easy-to-confuse things inside one subject, like different kinds of math problems. Switching from history to chemistry mostly gives you spacing, because each subject is revisited after a gap. That is still useful. Just do not expect the interleaving effect from switching unrelated subjects.
Is it better to study one subject a day or several subjects a day?
For keeping everything fresh, several a day usually works better. One subject per day means each subject waits several days for its next turn, and long blocks of one topic feel fluent without testing you. Two or three subjects a day keeps the gaps short and gives each one a regular, spaced review.
How many subjects should I study in one day?
Two or three is a practical number for most people. That is enough to keep each subject on a short rotation, and few enough that each block gets real focus. If you study more subjects in total, rotate them across the week so every subject comes up at least every few days.
Why does blocked practice feel better if it works worse?
Because it feels fluent. When you do ten problems of the same kind, you never have to work out which method to use, so it feels like learning. In one experiment of a 2008 study by Kornell and Bjork, 78 percent of people did better with mixed practice, yet 78 percent rated blocking as good or better.
The bottom line
Studying several subjects at once is not what makes you forget. Long gaps and smooth, blocked practice are. Rotating subjects fixes the gaps, mixing problem types inside a subject trains you to tell similar things apart, and an opening quiz shows what slipped.
Start this week. Put every subject on a rotation of two or three a day. Open each block with five minutes of recall. Mix your practice problems. End the week with one shuffled review across all of them. It will feel harder than finishing one subject at a time, and that is the sign it is working.
