Wrong answer.
What happened?
Your kid forgot how to do something, and so they made a mistake.
“What, it’s wrong? Arghh. I failed again. I’m a failure.”
Sadness and tears (used to, or maybe still do) ensue.
Perhaps even anger at themselves / math in general.
This is a real danger if your kid loves math and they forget something. It feels like getting an answer wrong because they forgot how to do something is a reflection of who they are and a value judgment of who they are as a person.
Some parents help instill in their kids the feeling that “if I am good at math, I am valued.”
Some kids instill that feeling in themselves (Hello, perfectionism!).
In either case, it’s not mentally healthy and misses the bigger picture.
Some kids go through it early, while others carry on this burden for part/most of their lives.
Today’s post is about “What to do when they forget something they *knew*”.
I. Start With the Reassurance: Forgetting Is Normal
While not helpful in the moment, it’s crucial to help kids understand that forgetting how to do this is normal and a part of the human experience.
It can also be helpful for you, as an adult, to remind yourself that forgetting something isn’t a sign of laziness or disrespect.
Overall, it’s not a character flaw in the child, it’s just something that happens.
Forgetting is how memory works and not a sign that something has gone wrong.
We’ll talk about it in the next section, but your brain and the kids’ brains are built to forget things they don’t use, so if it’s been a while since they used that math technique, the brain will eventually forget it.
So if a kid forgets something, it’s not that they’re bad at math, a failure, or should quit math.
It’s that they’re human, and their brain decided it didn’t need that bit of information.
The key message for your kid is that forgetting will happen.
Not if, but when and how often.
And that’s it perfectly normal.
And as adults, it’s up to us to model positive behavior, and how we respond, so the kid learns it’s not a value judgment and that it’s natural.
It means we have to work on helping our brain understand that we want to remember it.
You may even share when you forget something to show them that it happens frequently, in many different circumstances, and that it’s not the end of the world.
II. The Science: How Memory Works
In our household, it helped us learn a bit of the science behind how memory actually works.
Roughly speaking, there is a short-term memory system and a long-term memory system. (This is a simplification, but a useful one for our purposes.)
Short-Term Memory
Short-term memory can hold about seven items (plus or minus two) (Note that some modern studies say that the number is closer to 4 +/- 1).
So at any one time, you can remember 5 to 9 things.
Sure, you can chunk things to squeeze a bit more out of it (think about phone numbers: remembering “123” instead of “1” and “2” and “#”), but the roughly seven-item limit remains the same.
This is why cramming works (for a short while): you can cram things into your brain in chunks and then regurgitate them soon after.
Two reasons not to rely on short-term memory are that a) as new information enters, your brain throws out old information, and more importantly for math, short-term memory cannot support multi-step reasoning (which is basically what math involves).
Long-Term Memory
Long-term memory can hold an unlimited amount of information for long periods.
However, there are a few limitations (ignoring the biological one of the brain being a fixed, non-infinite size):
Difficulty in memory retrieval: Not all long-term memories are equally strong, and some may be harder to access than others
Memory cues: Retrieving information is often easier with prompts or “memory cues” that help activate the memory trace, much like searching for a file on a computer
Memory degradation: The accuracy of recalling information can decrease over time, not necessarily because of a limited duration, but potentially due to factors like age or interference from new information.
Which is where the forgetting happens if it’s a math technique that hasn’t been used in a while (which again, is perfectly natural).
Memory degradation follows a curve-like pattern rather than being linear.
The “forgetting curve” means it takes a while to forget something, but then it drops off sharply.
Short-Term to Long-Term
The name of the game, then, is to move things from short-term to long-term memory and to strengthen the retrieval patterns and memory cues.
There are many tools to help you move things into long-term memory, like our favorite, Anki.
The focus is on:
Remembering Math
Whether it’s Math or what your 1st grade teacher’s last name was, the brain stores all of the information pretty much the same way.
When the kid works on math and sometimes forgets it, it’s not that the kid is “forgetting math”, it’s that the kid’s brain is forgetting *a thing that happened to be math*.
Thus, knowing the science behind memory and forgetting (even this basic introduction) means that the kid (and you as the adult) are well equipped to help the kid understand scientifically what happened, why it’s normal, and how to improve it (such as working on your spaced repetition, doing more practice problems, and using retrieval practice like quizzing yourself).
The tricky thing, however, is that math builds upon itself, so “I forgot how to do the problem” isn’t as straightforward as one might think.
III. Math Has Many Steps, and Kids Forget Steps Differently
Roughly speaking, doing math involves a long chain of small reasoning steps.
Later in college and beyond, it moves to making a statement and rigorously proving whether it is true or false, again using a chain of small reasoning steps.
In either case, math involves a (short, medium, long) chain of reasoning steps.
So when the kid says “I forgot how to do the problem”, it’s not an all-or-nothing statement, as in “I know it” versus “I don’t”.
Even trickier is that there is a ladder of fluency in math that makes the “forgotten technique” issue even fuzzier.
We can think of the ladder of fluency as follows:
Seen it once and can recognize the problem and technique to be used
Can setup the problem solving strategy and start it
Can do all the steps with help
Can do all the steps on their own but slowly
Can do the steps accurately but not automatically (think having to skip count by 8 to figure out the 7*8 multiplication, rather than remembering that 7*8 = 56)
Can do it easily, fast, accurately, every time
And since each kid will be on a different rung of the ladder for every single math technique, it’s harder to pinpoint exactly what was forgotten / where and how to help.
Which means we/you/the kid has to dig deeper to figure out precisely what was forgotten.
Which is why teachers in school tend to be super pedantic about a) neat writing, b) writing down your thinking process, and c) writing down each and every step.
IV. Why Writing Every Step Helps
Writing out all the steps lets you/the kids see exactly *where* things fell apart or how far they got before they couldn’t do anything else.
Note that if you do math with the kid by sitting next to them, it also lets you see what steps of the reasoning were fast vs slow, and what steps had to be redone as the kid remembered something they should have done earlier (especially in early math things like negative signs, parentheses, converting fractions, and so on).
Additionally, this process helps teach the kid how to self-coach when they work alone later by noticing what was easy for them and what was hard.
If it was easy, then I don’t need to work on that skill.
If it was hard, then I need to work on making that memory easier to retrieve.
If it was impossible, then I need to go back to figure out what I forgot.
Bringing back the science of memory: if each step in a solution is already in long-term memory, then the brain is freed up to focus on the *new* technique that’s being learned right now.
Let’s look at the impossible-to-figure-out-how-to-proceed step where they got stuck or got it wrong.
V. When They Forget: Diagnose the Right Problem
Kids rarely forget the technique itself, they just forget a prerequisite step.
For example:
Trouble with multiplication → underlying trouble with repeated addition *or* with 2-digit mental addition.
Trouble with negative signs → underlying trouble with inverse operations
Trouble with fractions → underlying trouble with factoring or Lowest Common Multiple
This is why “I forgot how to do this problem” often really means “I forgot one small piece that everything else depends on.”
Which means that to help them remember it, you and they need to go backwards to figure out the last point they fully remember.
It’s best to go backward, one unit/concept at a time, to make sure you aren’t covering material they already remember.
Then, when you do find it, you want to move forward slowly until you hit the *exact* gap in their knowledge.
Once you find that, you cement that knowledge through various means (the next section covers this) to improve the accuracy of the kids’ thinking.
This builds confidence and helps them learn how to recover from “forgotten” math knowledge.
VI. The Review Strategy Works That For Us
Three things we want to focus on when go back to figure out how to fix the issue.
*We want to make it very clear to the kid that there is no shame and nothing wrong with them for forgetting.*
We want them to stop spiraling if their emotions are getting too big for them to handle.
We also want to make sure we focus only on the missing piece and nothing else, because that’s what was forgotten, so we/they won’t waste time reteaching/relearning everything.
The review pattern is roughly as follows:
Go back 2–3 chapters before the “forgotten” skill.
Do a few examples from earlier material to warm up.
Move forward gradually until we hit the forgotten step.
Celebrate rediscovery (“oh right, that’s the part I forgot!”).
Re-teach or re-practice just the missing piece.
Do a handful of new problems to refresh long-term memory.
Sometimes this will be quick, and sometimes (we’ve been there!) it’ll take a few weeks to internalize the technique again.
Whether the forgetting is resolved in the short or long term, both are normal and highly dependent on the child.
Again, there is nothing wrong with the kid when they forget something, and if it takes them time to re-learn the skill.
They’re a math-loving kid, so it should always be shaped as a fun (re-)exploration of the topic.
Sometimes you might have to do this two or three (or more) times with the same topic, and that’s okay.
Two things you may run into if it’s a highly-specific technique or if the resource you’re using (worksheets, book, website) are that a) you can’t find enough new problems to work on the technique, or b) you/the kid need another way to explain the technique.
Luckily, we live in the age of LLMs and AI.
VII. Use AI as a Gentle Diagnostic and Problem Creation Tool (Not a Crutch)
We don’t want to train the kid to use AI to find answers to math problems because doing math problems is the whole point of learning math.
What we do want to help train the kid on is how to use the LLMs/AIs effectively to help the learning process.
Especially knowing that today’s algorithms can provide wrong answers, hallucinate things that aren’t real, and may be built on shaky moral/legal grounds.
To that end, use the AI to ask for only the next step, not the whole solution.
*Remember that you are diagnosing what was forgotten, not having it show you how to do the problem.*
Once you know where the memory gap was, you can use the AI to generate basic to intermediate problems explicitly focused on that exact step.
This helps focus the learning time and ensures the right thing is practiced to help it move from short-term memory to long-term memory.
As a bonus, if it’s not shown in the book, you can ask the AI to help show how a specific math technique/fact can be derived.
VIII. Re-Derive, Don’t Just Re-Memorize
When you/the kid work through re-deriving the example, it’ll help connect to more things within their existing memory structure which will make it easier to remember in the future.
Three examples that fit here are:
Arithmetic: Multiplication as repeated addition
High School Algebra I: Quadratic formula
High School Geometry: Area of an equilateral triangle
In each case, the kid can memorize the fact/formula, but they’ll be much better served if they go through the derivations a few times, especially if they forgot them.
The re-derivation helps train them in mathematical reasoning, strengthens connections to other topics they’ve seen before, and reduces the fear of forgetting, since they can always re-derive it if need be.
This can also help you with kids who really want to know why something works.
Obviously, you may not have time to rederive everything from scratch/first principles every time, but if a topic is often forgotten, it’s well worth spending the time there.
Over time, this will become one of the strongest “maturity builders.”
Speaking of building maturity, when a kid forgets something and gets upset, or when they share work with you and you notice where they forgot, emotions will run high.
IX. Emotional Work: No Shock, No Anger, No Value Judgment
Emotions will run high for both parent AND child.
I’ve been there and incredulously asked, “How could you even forget that?!”
I may have even demanded an answer to, “Why did you forget that?!”
I’ve definitely let my frustration run away with me.
I, too, am human, and it’s hard to remember in the moment that the kids already feel rotten about having forgotten something.
My/your inquisition will not help them.
It usually just adds shame on top of confusion.
This makes their emotions run even higher/hotter and makes it less likely that they’ll be able to reason through it.
Instead, we (and hopefully they in the long run) need to remember that forgetting is expected, that it lets us review topics we enjoyed learning in the past, and that it has no merit on who we are as a person or student of math.
And if your frustration gets the better of you, apologize right away.
I always apologized and explained my surprise.
While I may not longer get mad/sad/frustrated, I still do get surprised.
But now I have a plan (the above), and we will work through it.
While it may seem like a small thing, being able to recover is a great “life practice” that will help the kids with homework, tests, college, and life down the road.
Forgetting will happen again in the future.
X. Build the Habit of Leaving Notes for Their Future Self
To help guide them in their reasoning and to help them understand, it can be helpful to ask them to leave notes for their future self in case they forget again.
The explanation should be in their own words, relating what they forget and how to remember it.
Be sure to encourage them by creating examples that helped them understand.
This way, if they forget again, they have a friend waiting for them on the page: their past self.
This works wonderfully because it teaches self-coaching, autonomy, and long-term resilience.
It also means they use language that makes sense to them so if/when they look at it again later, they will probably have an easier time understanding the examples.
And like the other skills above, they can continue to use this technique in a myriad of subjects and in life.
XI. Conclusion: Forgetting happens, so have a plan
Forgetting is part of learning, and the sooner you and your kid accept it and have a plan for handling it, the better the emotional outcomes you and they will achieve.
The goal isn’t to never forget (though Anki can really help here), it’s to know what to do when the kid forgets something.
Lead with kindness (self-love) and remind the brain that it actually did need that piece of information.
Everyone, from kindergarteners to professional mathematicians, forgets from time to time, and that’s just life in mathematics.
XII. Closing
That’s all for today :) For more Kids Who Love Math treats, check out our archives.
Stay Mathy!
Talk soon,
Sebastian
PS What’s something you or your child “forgot” that surprised you? Hit reply or comment.