There's a particular kind of frustration that most parents of primary-age children will recognise. Your child spends an evening working through a topic. They seem to get it. Then a week later, when you casually ask about it, they look at you like you've invented the question from scratch.
It's not laziness. It's not a lack of effort. It's something far more fundamental – and once you understand it, you can actually do something about it.
The curve that explains everything
In the 1880s, a German psychologist called Hermann Ebbinghaus did something unusual: he spent years memorising lists of nonsense syllables – things like "WID" and "ZOF" – and then testing how quickly he forgot them. He wanted to strip memory down to its bare mechanics, free from anything meaningful that might help him cheat the results.
What he found has shaped how we think about learning ever since.
Ebbinghaus plotted how memory declines over time on a graph, creating what he called the forgetting curve. The shape is striking. After learning something new, you forget around 50% within the first 30 minutes. Within 24 hours, that rises to 70–80%. And without any kind of review, you can lose up to 90% of what you learned within a week.
That's not a flaw in your child's brain. It's how all brains work.
The forgetting curve has been replicated many times since Ebbinghaus first published his findings. A modern replication, which had participants spend 70 hours learning and relearning lists at intervals ranging from 20 minutes to 31 days, produced results closely matching Ebbinghaus's original data. The curve is real, and it applies to all of us.
The steep drop at the start
The most important thing to understand about the forgetting curve is that most of the forgetting happens immediately.
Memory declines exponentially in the initial hours and days after learning, then gradually levels off. In other words, a child who sits down to revise on Sunday evening but doesn't encounter that material again until the following weekend has already lost the majority of it before Monday morning.
This is why cramming doesn't work – not just for exams, but for real learning. You can pack information in. It just doesn't stay.
Why some things stick and others don't
Not all memories fade at the same rate. Ebbinghaus recognised this himself, which is part of why he chose meaningless syllables – he didn't want meaningful associations to distort his results.
Knowledge that is well-integrated into what a child already knows is far more resistant to forgetting. A child who understands why long division works will remember it more reliably than one who has memorised a sequence of steps without any sense of what they mean.
Other factors also affect how quickly information fades: how difficult the material is, how it's represented, and physiological factors like stress and sleep. A child who is anxious, tired or overwhelmed is fighting the forgetting curve from a harder starting position.
What actually works: spaced learning
The best remedy Ebbinghaus found wasn't studying harder or for longer. It was timing the review.
He found that with each repeated exposure to material, the speed of forgetting slowed significantly. The goal of spaced repetition is to revisit that material when it's starting to fade – but before it's gone entirely. For most learners, that means returning to newly learned material one or two days after the first encounter.
Each review reshapes the forgetting curve, making it progressively flatter. Over time, the intervals between reviews can grow longer while retention remains strong.
The practical implication for parents is simple: a little bit, often, beats a long session once a week. A child who spends 15 minutes on a topic on Monday and revisits it briefly on Wednesday and again on Friday will retain far more than one who does an hour on Sunday and nothing else.
That's why HeyKisu is built with spaced repetition in mind: it's been calibrated to surface topics repeatedly over time to increase learning and recall.
Active recall beats re-reading
There's a second finding from cognitive science that's just as important: the testing effect.
Research consistently shows that actively retrieving information from memory strengthens learning more effectively than simply rereading material. This process improves long-term retention by strengthening neural connections. In educational contexts, this is why frequent low-stakes practice questions can significantly improve learning outcomes.
Re-reading notes feels productive. But it's largely passive – your child is recognising information, not retrieving it. Answering questions, explaining a concept in their own words, or working through problems from scratch all require active retrieval. That's what builds durable memory.
When you ask your brain to retrieve information, you solidify the connections between neurons more and more each time, and the information moves from short-term working memory into long-term memory.
That's why HeyKitsu is so successful: continual testing of concepts ensures your child will remember on test day.
Keep sessions short
One more thing Ebbinghaus's work points to: cognitive overload is the enemy of retention.
When children are given too much information at once, or pushed through long, unbroken sessions, their working memory gets overwhelmed. Reviewing content in varied contexts and formats – quizzes, practice problems, different types of question – enhances the richness of memory traces and prevents rote memorisation.
HeyKitsu recommends short sessions of 15–20 minutes, spread across the week. These are much more effective than longer sessions crammed into the weekend. It's less about volume and more about consistency.
A note on pressure
All of this has one more implication worth naming directly: stress makes the forgetting curve worse.
Ebbinghaus hypothesised that physiological factors like stress and sleep affect the basic rate of forgetting. A child who is anxious about the 11+ isn't just less happy – they're less likely to retain what they've worked hard to learn.
Building in rest, keeping sessions low-stakes and maintaining a consistent sleep routine aren't luxuries. They're part of the learning strategy.
How HeyKitsu is designed around this
We built HeyKitsu with the forgetting curve in mind. The platform's adaptive engine doesn't just track what your child has covered – it tracks what they're likely to be forgetting, and brings topics back at the right moment. Practice questions are spaced, low-stakes and varied in format. Sessions are short by design.
The goal isn't to drill children into exhaustion. It's to give their memory the conditions it needs to actually work.
If you want to see how it works in practice, the first three levels in every topic are permanently free – no trial period, no credit card, no expiry. Try it with your child and see whether it feels different from sitting down with a revision workbook.
If you're interested in the original research, Ebbinghaus's 1885 paper – "Über das Gedächtnis" (Memory: A Contribution to Experimental Psychology) – is surprisingly readable for a Victorian-era psychology text. The 2015 replication study in PLOS ONE is also worth a look if you want to see how the curve holds up under modern scrutiny.
Written by
HeyKitsu Team