Interleaving topics in secondary science: how mixing practice improves final grades

When preparing students for GCSE science exams, the standard departmental approach seems entirely logical. Teach biology topic 1 in full, assess it, move on to topic 2, assess it, and repeat the process through chemistry and physics. When revision season arrives, timetables usually follow the same linear pattern: biology on Monday, chemistry on Tuesday, physics on Wednesday.

This approach is known as blocking (or blocked practice). While it feels organised and reassuring to both teachers and students, research suggests that blocking is often less effective for long-term retention than interleaving. Interleaving is the deliberate practice of mixing related subjects or topics within a single study session. A meta-analysis of 59 studies found a moderate overall benefit for interleaving, with the strongest effects when the things being mixed are easy to confuse with one another [1].

For secondary science departments aiming to raise attainment across AQA, Edexcel or OCR specifications, shifting from blocked revision to systematic interleaving is one of the most useful changes available.

• Blocked practice (one topic at a time) feels productive, but interleaved practice usually leads to better long-term recall.

• Exams mix topics, so students need practice at choosing the right method, not just repeating one.

• Start small: mixed starters, split revision sessions and cumulative homework.

Blocking allows students to stay within a single conceptual framework for an extended period. If a student spends 2 hours working through 20 consecutive questions on quantitative chemistry, every answer relies on the same formula. The student does not need to choose which strategy to apply. They simply execute the same procedure over and over.

This creates high immediate performance during the session, giving the student a false sense of mastery. Students are often fooled by it: in one well-known study, participants rated blocked study as more effective than interleaved study, even after their own test results had shown the opposite [2].

However, real GCSE science papers do not present questions in neat, predictable blocks. A student might face a question on electrolysis, followed immediately by one on plant cell adaptation, followed by vector forces. The main challenge in an exam is not just executing a calculation or recalling a definition. It is telling problem types apart and selecting the correct mental schema under pressure.

• Blocked revision (AAA BBB CCC): high immediate confidence during study, but poor discrimination on exam day.
• Interleaved revision (ABC BCA CAB): higher initial mental effort, but better long-term exam retention.

Interleaving forces the brain to keep categorising problem types, which builds stronger exam recall than blocked revision alone.

Interleaving forces the brain to keep reloading information into working memory. When a student switches from an organic chemistry question to an energy transfers physics problem, the brain has to put aside the previous rule set and retrieve the appropriate conceptual framework from long-term memory.

This process feels harder and messier for the student. Performance during the practice session might drop slightly compared with blocked practice. However, as Robert Bjork’s research on desirable difficulties shows, this added friction is precisely what strengthens memory and improves problem-solving discrimination.

This is not just a laboratory effect. In an 8-week study in an introductory university physics course, students whose homework problems were interleaved recalled more relevant information and produced correct solutions more often on 2 surprise tests, with median improvements of 50% and 125%. They also rated interleaving as harder and wrongly believed they had learned less from it [3].

When students interleave their practice:

• They learn to identify the subtle cues that signal which scientific law or equation applies.
• They build stronger cross-topic connections (such as linking biological respiration to chemical exothermic reactions).
• They become far more resilient when they meet unexpected question combinations on real exam papers.

Interleaving is not a magic switch. The same meta-analysis found that it works best when the topics being mixed look alike but need different approaches, and it found no benefit, or even a cost, for some materials such as word lists [1]. In science, that makes problem-solving and calculation topics the natural place to start.

Introducing interleaving does not require rewriting your entire scheme of work. Subject leaders and classroom teachers can make small, high-impact changes tomorrow:

Replace single-topic starter tasks with 5-minute mixed starters containing one question from biology, one from chemistry and one from physics, drawn from topics covered earlier in the term or year.

Advise students against 2-hour single-subject revision blocks at home. Instead, guide them to split a 45-minute session into three 15-minute segments covering three distinct science topics (for example, 15 minutes on cell mitosis, 15 minutes on ionic bonding and 15 minutes on specific heat capacity).

Make sure weekly homework sets regularly pull in questions from previous units rather than focusing only on the content taught that week. Combined with low-stakes retrieval practice, this keeps older topics alive until the exam.

Manually organising an interleaved study schedule across three science disciplines is a heavy load for teachers and overwhelming for students. Tassomai solves this by building interleaving into its core algorithm.

• Automatic topic switching: Tassomai’s algorithms are designed around spaced and interleaved quizzes with instant feedback and adaptation, so each student’s daily practice mixes topics from across the course based on what they know and what they don’t.
• The understanding grid: teachers can see at a glance where knowledge is secure and where gaps are showing, topic by topic, across a whole class. See how the understanding grid works.
• Group Quiz for class starters: teachers can launch a Group Quiz targeted at their class’s weakest topics in about 10 seconds, and every question is then blended back into students’ individual daily practice.
• Mai, the AI tutor: when mixed practice exposes a misconception, Mai gives students step-by-step guidance on the spot.

By taking the scheduling burden off teachers, Tassomai turns complex cognitive science into a simple daily habit for students. See how Tassomai works for science departments.

Ready to bring interleaved retrieval practice to your science department? Book a demo with the Tassomai team.

1. Brunmair, M., & Richter, T. (2019). Similarity matters: A meta-analysis of interleaved learning and its moderators. Psychological Bulletin, 145(11), 1029-1052. https://doi.org/10.1037/bul0000209
2. Kornell, N., & Bjork, R. A. (2008). Learning concepts and categories: Is spacing the “enemy of induction”? Psychological Science, 19(6), 585-592. https://doi.org/10.1111/j.1467-9280.2008.02127.x
3. Samani, J., & Pan, S. C. (2021). Interleaved practice enhances memory and problem-solving ability in undergraduate physics. npj Science of Learning, 6, Article 32. https://doi.org/10.1038/s41539-021-00110-x