The Study Science That Actually Works: Spaced Repetition and Retrieval Practice
Every year we get the same question from parents, usually around February of third year or fifth year: is my child studying properly? Not studying enough. Studying properly. It is a fair question, and it has a better answer than most people realise, because how memory behaves under exam conditions is one of the more thoroughly researched topics in psychology.
What follows is what the evidence supports, what it supports less strongly, and where it genuinely runs out. We have tried to be honest about that third category, because it is where most study advice quietly stops being evidence and starts being opinion.
Ebbinghaus and the Shape of Forgetting
The starting point is Hermann Ebbinghaus, who in 1885 published Uber das Gedachtnis (On Memory), based on experiments he ran on himself using lists of nonsense syllables, chosen precisely so that no prior familiarity could help him. By measuring how much he had to relearn at intervals from twenty minutes out to thirty-one days, he produced what is now universally called the forgetting curve: retention falls steeply at first, then flattens.
Two things about it are worth knowing. The first is that it has held up. Murre and Dros published a replication in 2015 using Ebbinghaus's original method and obtained a closely matching curve. The second is that Ebbinghaus also identified the spacing effect: material reviewed at intervals is retained better than the same quantity of study crammed together. That single observation, made before the modern exam system existed, is still the most useful thing a student can know.
Retrieval Practice: Testing Yourself Is Studying
The second pillar is the testing effect. The reference point most people cite is Roediger and Karpicke's 2006 paper in Psychological Science, Test-Enhanced Learning: Taking Memory Tests Improves Long-Term Retention.
Their design matters more than the headline. Students studied prose passages and then either took repeated free-recall tests with no feedback at all, or reread the material the same number of times. Everyone was tested again after five minutes, two days, or one week. After five minutes, rereading won. After two days and after a week, the students who had tested themselves retained substantially more.
That reversal is the whole point, and it explains a pattern we see constantly. Rereading produces a strong feeling of familiarity immediately afterwards. Retrieval feels harder, feels less satisfying, and works better later. The exam is later.
The Review That Ranked Ten Techniques
In January 2013, John Dunlosky, Katherine Rawson, Elizabeth Marsh, Mitchell Nathan and Daniel Willingham published a review in Psychological Science in the Public Interest assessing ten commonly used study techniques and rating each as high, medium or low utility.
Two were rated high utility: practice testing, and distributed practice, meaning study spread out over time. They earned that rating because the benefit held across different ages, ability levels and subject areas, which is a considerably stricter bar than working once in one experiment.
Rated low utility: rereading, highlighting and underlining, and keyword mnemonics. The authors' objection was not that these never help anyone. It was that they are difficult to implement well and produce inconsistent gains. Highlighting is close to universal among Irish students and close to useless as a primary method, because deciding what to highlight is a much lower-effort operation than deciding what a passage actually means.
Interleaving, Which Is More Conditional
Interleaving means mixing problem types within a practice session rather than working through twenty of one kind in a block. Rohrer and Taylor's work in mathematics is the clearest demonstration: students given mixed problem sets performed worse during the practice session itself and substantially better on a test given later.
We would flag this one more carefully than the other two. The 2013 review placed interleaving in its middle category rather than alongside practice testing and distributed practice, and the strongest evidence comes from mathematics and from category-learning tasks. Whether it transfers cleanly to, say, a Leaving Cert History essay is not something the research settles. Treat it as well supported for maths, applied maths and the problem-based sciences, and as a reasonable experiment elsewhere.
What This Looks Like in a Real Study Week
Translating this into something a fifteen-year-old will actually do:
- Close the book and write down what you remember before you look anything up. That single change converts passive revision into retrieval practice.
- Return to each subject at intervals rather than in one long block. Four thirty-minute sessions across a fortnight beat one two-hour session.
- Use past papers as a learning tool from the start of the year, not as a dress rehearsal in the last three weeks.
- If you highlight, treat it as the first step and never the last. Something has to happen to the highlighted material afterwards.
- In maths and the sciences, mix question types within a session, and expect it to feel worse while you are doing it.
Where the Evidence Stops
Some honesty is owed here. Much of this research was conducted on undergraduates, in controlled conditions, using material chosen by the researchers. It was not conducted on Irish sixteen-year-olds revising nine subjects for a state examination. The direction of the findings is robust and replicated. The exact size of the effect in a Junior Cycle Geography module is not something anyone has measured.
Nor does any of it address motivation, sleep, anxiety, or a household in which studying is difficult, and those frequently matter more than technique does. Spacing and retrieval will not rescue a student who is not studying at all. What they will do is ensure the hours already being spent produce something more durable than a feeling of familiarity.
Retrieval practice and spaced revision are built into the structure of every title in the Irish Exam Guides series, and they are the subject of Study To Succeed, which sets out the full method with schedules and worked examples for both Junior Cycle and Leaving Cert.