When you sit down to study for your CCNA, the intuitive approach is to take Chapter 7 on OSPF, read it through, do the exercises at the end, watch the supplemental video, then move on to Chapter 8 on BGP. You complete one topic before starting the next. This feels logical — master each concept in sequence, build a clean foundation, avoid confusion. It is also, according to decades of cognitive research, a significantly less effective approach than the alternative.
That alternative is interleaving: deliberately mixing topics within a study session instead of blocking them. Studying OSPF, then VLANs, then NAT, then back to OSPF, then STP — in a single session, without completing any one of them before moving to the next. This feels counterproductive. Your performance during those sessions is visibly worse than in blocked sessions. And yet, on delayed tests and real exams, interleaved learners consistently outperform blocked learners by substantial margins.
Understanding why interleaving works — and how to apply it to certification study — requires looking at what your brain actually does when it has to switch contexts repeatedly.
The cognitive mechanism behind interleaving
Blocked practice creates a particular kind of learning trap. When you study one topic continuously, your brain builds a context cue: this is the OSPF session, so everything in working memory is OSPF-related. Problem-solving becomes easier because the context itself tells you which tools to reach for. You are not learning to recognize when to use OSPF; you are just practicing OSPF-specific procedures in an OSPF-specific environment.
Interleaving removes the context cue. When you have just finished three OSPF problems and then encounter a routing problem, you must first determine what kind of routing problem it is — is it OSPF, EIGRP, static routing, or a redistribution scenario? That discrimination step is cognitive work you would not have done in a blocked session. And that work is precisely what certification exams require.
A 2010 study by Rohrer and Taylor found that students who practiced math problems using interleaved sets scored 43% higher on a delayed test than students who practiced the same problems in blocked sets. Both groups had the same total practice time. The interleaved group showed worse performance during practice and dramatically better performance on the actual test.
"When students interleave their practice — mixing different problem types within a session — they develop the discrimination skill that examinations actually require. They learn to identify what kind of problem they are facing before they solve it. Blocked practice skips that step, producing fast solvers of already-identified problems." — Doug Rohrer, Applied Cognitive Psychology, 2012
This gap — worse during practice, better on tests — is the hallmark of a desirable difficulty. The struggle during interleaved practice is not noise; it is the learning signal.
Why blocked study feels better and performs worse
Blocked study produces a reliable feeling of fluency and progress. After spending forty minutes on VPC subnetting, you can solve VPC subnetting problems smoothly. That smooth performance triggers a sense of competence and mastery. The feedback loop is positive and immediate.
What blocked study does not produce is discrimination skill — the ability to look at a problem and identify what type of problem it is. In blocked practice, that identification is automatic. In an exam, it is not.
The AWS Solutions Architect Associate exam, for instance, frequently presents architecture scenarios without labeling what concept is being tested. A question about a high-traffic application with latency requirements might be testing CloudFront, Elasticache, Auto Scaling, or read replicas — or some combination. Candidates who blocked their studies — doing all CloudFront topics, then all Elasticache topics — often know each service well but struggle to decide which one applies.
Candidates who interleaved their practice have encountered exactly this discrimination problem during study. They have already practiced identifying which tool fits which scenario.
Applying interleaving to different certification tracks
CCNA and CCNP
Cisco exams test networking concepts that interact heavily with each other. Switching, routing, security, and wireless are not independent domains — they appear in combined scenarios on the exam.
An interleaved study session for CCNA might cycle through:
- 20 minutes of OSPF neighbor formation review
- 20 minutes of STP port state troubleshooting
- 20 minutes of VLAN and trunking configuration review
- 15 minutes of ACL troubleshooting scenarios
- 15 minutes back to OSPF, now focusing on metric calculation
Switching between these every 15-20 minutes prevents the context cue from forming and forces continuous discrimination: is this a Layer 2 or Layer 3 problem? Is this a connectivity issue or a loop prevention issue?
CompTIA Security+
Security+ covers a wide range of domains — cryptography, identity management, network security, risk management, incident response — that all interact in real security scenarios. Interleaved practice sessions should draw from multiple domains.
A useful approach: build a pool of 100 practice questions across all domains and work through them in randomized order rather than domain-by-domain. Domain-by-domain drilling inflates your apparent performance (you know it is a cryptography question before you read it) while interleaved practice tests the ability to identify the domain from context alone.
AWS and Azure certifications
The association exams (AWS SAA-C03, AZ-104) benefit enormously from interleaved practice because their scenario questions explicitly mix service categories. Study sessions that jump between compute, storage, networking, and security — rather than completing each service category before moving on — develop the cross-domain reasoning skills the exams require.
A specific interleaving technique for AWS: create a practice set with one question from each of the five domains in the exam guide, repeat until you have 50 questions, and work through them in that mixed order. The artificial domain-jumping recreates the discrimination challenge of the actual exam.
Scheduling interleaved study
Interleaving works best when planned deliberately, because the natural tendency is to block.
One practical framework is the "card deck" approach: write each topic you are currently studying on a separate index card. At the start of a study session, shuffle the cards and work through them in that order, spending 15-25 minutes on each before the next card comes up. When you return to a topic, you are doing a de facto retrieval practice session — you need to recall where you were and what the key concepts are before diving back in.
This approach also serves as a spaced repetition mechanism if you keep the same cards across multiple sessions. Topics you understand well can be shuffled to appear less frequently; topics with remaining gaps can be added as duplicates.
Another approach: use a rotation schedule.
| Week | Session 1 | Session 2 | Session 3 |
|---|---|---|---|
| Week 1 | Topics A, B | Topics B, C | Topics A, C |
| Week 2 | Topics A, B, C | Mixed practice questions | All topics: mini-quiz |
| Week 3 | Topics D, E | Topics D, A, B | Topics C, E |
The goal is to prevent any topic from going more than two days without some form of retrieval practice, while avoiding the prolonged same-topic sessions that blocked study creates.
The spacing-interleaving combination
Interleaving and spaced repetition are distinct but complementary strategies. Spaced repetition controls when you revisit a concept (optimally spaced intervals to exploit the forgetting curve). Interleaving controls how you practice within a session (mixed rather than blocked). Used together, they address different aspects of the encoding problem.
A study session built around both principles might look like this: your Anki deck (spaced repetition) shows due cards from multiple domains — some you reviewed last week, some from yesterday, some from this morning. Working through those due cards in the order Anki presents them is already an interleaved session by nature. The algorithm has already mixed the topics optimally.
For candidates who do not use spaced repetition software, building manual review sessions that explicitly draw from multiple topics is the closest equivalent.
Managing the discomfort
The most consistent feedback from candidates who switch from blocked to interleaved study is that the early sessions feel chaotic and unproductive. Performance drops visibly. It becomes harder to feel confident about any single topic because you keep moving before the fluency feeling arrives.
That fluency feeling is precisely what you should be suspicious of. In blocked study, fluency comes from context cues, not real understanding. The absence of that feeling during interleaved study is not a sign you are learning less — it is a sign you are learning more genuinely.
A practical way to track real progress: after each interleaved session, spend five minutes writing down what you remember from each topic you covered. The quantity and accuracy of what you can retrieve — not how smooth the session felt — is your actual performance metric.
See also: Retrieval Practice Techniques: The Most Effective Way to Study for Exams
References
- Rohrer, D., & Taylor, K. (2010). The effects of interleaved practice. Applied Cognitive Psychology, 24(6), 837-848.
- Brown, P. C., Roediger, H. L., & McDaniel, M. A. (2014). Make It Stick: The Science of Successful Learning. Belknap Press. ISBN: 978-0674729018.
- Taylor, K., & Rohrer, D. (2010). The effects of interleaving practice. Applied Cognitive Psychology, 24(6), 837-848.
- Kornell, N., & Bjork, R. A. (2008). Learning concepts and categories: Is spacing the "enemy of induction"? Psychological Science, 19(6), 585-592.
- Carey, B. (2014). How We Learn: The Surprising Truth About When, Where, and Why It Happens. Random House. ISBN: 978-0812993882.
- Dunlosky, J., Rawson, K. A., Marsh, E. J., Nathan, M. J., & Willingham, D. T. (2013). Improving students' learning with effective learning techniques. Psychological Science in the Public Interest, 14(1), 4-58.
- Bjork, E. L., & Bjork, R. A. (2011). Making things hard on yourself, but in a good way: Creating desirable difficulties to enhance learning. In M. A. Gernsbacher et al. (Eds.), Psychology and the Real World. Worth Publishers.
Frequently Asked Questions
What is interleaved practice and how is it different from blocked study?
Blocked study means completing all practice on one topic before moving to the next — finishing all OSPF problems before starting STP, for instance. Interleaved practice means mixing topics within a session — some OSPF, then some STP, then some VLAN problems, then back to OSPF. The mixing prevents your brain from using topic context as a shortcut, which forces the discrimination skills that exams actually test.
Why does interleaved practice feel harder if it produces better results?
Blocked study creates processing fluency — you are solving problems in a context that tells you exactly what type of problem they are. That fluency feels like mastery. Interleaved study removes that context cue, so each problem requires more effort to classify and solve. The effort feels like struggle, but it is the learning signal. Cognitive scientists call this a 'desirable difficulty' — harder during practice, much better on delayed tests.
How do I apply interleaving to AWS or Azure certification study?
Build practice question sets that draw from multiple domains rather than drilling one service category at a time. For AWS SAA-C03, mix compute, storage, networking, database, and security questions in the same session. Use randomized practice exams rather than domain-filtered ones. When reviewing course material, deliberately switch to a different service or domain every 20-25 minutes instead of completing entire modules.
Does interleaving work for hands-on lab practice as well as theory?
Yes. For hands-on certification prep — CCNA labs in Packet Tracer, Kubernetes CKA labs, or AWS console practice — interleaved lab sessions where you rotate between configuration types build stronger procedural memory than blocked sessions. For the CKA exam in particular, where you must quickly identify which kubectl commands apply to different problem types, interleaved kubectl practice is directly beneficial.
How long should each topic block be in an interleaved session?
Most research supports topic blocks of 15-25 minutes for cognitive subjects. Blocks shorter than 10 minutes do not allow enough depth to produce meaningful learning. Blocks longer than 30 minutes start to resemble blocked practice and reduce the discrimination benefit. For hands-on labs, 20-minute blocks per configuration task tend to work well. Adjust based on concept complexity — a simple concept might only need 15 minutes while a complex multi-layer scenario might warrant 25.