DEV Community: yoan ante

The bug I kept seeing in math practice: right answers that were too slow

yoan ante — Thu, 28 May 2026 18:05:32 +0000

I kept running into the same weird problem while helping my daughter with math.

She could get the answer right, but it took too long.

That sounds small until you watch what happens next. The new lesson is supposed to be about multi-step problems, division, fractions, or whatever the class is doing that week. But the kid is burning half their working memory rebuilding 7 x 8 in the middle of it.

So the worksheet looks like a concept problem, but the actual bottleneck is recall.

The right answer was not the whole signal

A lot of math practice treats "correct" as the full story. If the child eventually says 56, the box gets checked.

At home, that was not enough information.

There is a big difference between:

knowing 7 x 8 immediately
skip-counting up to 56
remembering a trick after a pause
guessing, checking the pattern, then landing on the right answer

Only the first one really frees the child up for the next part of the problem.

That is the part I wanted to capture when I started building Math Builders. I did not want another noisy drill screen. I wanted a small practice loop that could tell the difference between "this fact is automatic" and "this fact is technically correct, but still being rebuilt."

Why I used a 3-second threshold

The exact number is not magic. I used 3 seconds because it is a practical cutoff.

If a basic fact takes longer than that, the child may still know it, but it probably is not automatic enough to stay out of the way. That matters in real school work. Slow recall stacks up fast.

A kid can survive one slow fact. Five slow facts inside a longer problem turns into frustration.

That is where parents and teachers sometimes misread the situation. We see the struggle on the bigger assignment and start explaining the bigger concept again. Sometimes that is needed. But sometimes the child already understands the concept and the small facts underneath are stealing all the attention.

The product lesson for me

This turned into a product-design problem, not just a math problem.

If I only saved right and wrong, the app would miss the main thing I cared about. So the practice loop had to track speed and accuracy together, then keep bringing back the facts that were slow or missed.

That is basically the boring part of spaced repetition: do not make the parent or teacher manually remember which facts are shaky. Let the system keep a small review pile and make the next session predictable.

The boring part is the useful part.

A lot of kids do not need a bigger math block at home. They need a tiny one that does not turn into a fight. Two to five minutes, mixed facts, stop before everybody is annoyed, then come back tomorrow.

That was the shape I wanted:

short sessions
one clear task
no speed-race feeling
slow facts come back
fluent facts stop wasting time

What teachers already know

Teachers see this all the time. A student looks fine in a unit when the facts are isolated, then struggles when the same facts show up inside something messier.

That does not always mean the child forgot multiplication. It can mean the recall was never automatic enough to survive the messier context.

This is why I like the phrase "fake fluency." It is not that the child is pretending. It is that the practice data can look better than the real classroom behavior.

Correct-but-slow is the quiet version of that problem.

Where Math Builders fits

I am still building this as one person, and I am not pretending it has some huge classroom story behind it. It started because I needed a calmer way to help my own kid practice.

The current multiplication fact fluency page is here:

https://mathbuilders.com

If you are building learning tools, the lesson I would pull from this is simple: the most useful signal is not always the score. Sometimes the useful signal is the hesitation right before the right answer.

That is the part the kid feels, the parent sees, and the next worksheet punishes.

What I learned building a math fact app for my third grader (and why the 3-second threshold mattered)

yoan ante — Tue, 12 May 2026 15:04:16 +0000

I'm a developer in New Jersey. About a year ago my daughter, who was in third grade, was hitting the wall on basic math facts. She knew the strategies. She could derive an answer. But the recall was slow enough that anything that depended on the fact, word problems, division, fractions, was eating up all her working memory and crashing the rest of the problem.

I tried the apps everyone tries. Xtramath, Reflex, IXL, Prodigy. They all do practice, and they all give you a session percentage at the end. None of them did the thing I actually needed. Some of them I don't even know how they are allow to call themselves educational apps. Looking at you Prodigy.

So I built it.

The mechanic

The engine is a speed adaptive Leitner plus SM-2 hybrid. Each fact lives in a box. Get the fact right in under three seconds, the fact promotes one box and the interval to the next time she sees it widens. Get it right in three to five seconds, the fact stays in the current box. Take longer than five, the fact demotes two boxes. Wrong, reset to box one. Combined with the spaced reintroduction, the slow facts keep cycling back at short intervals and the fast ones move out of the active queue.

Three to five minute sessions. Stop anytime. That part is non negotiable, because the moment a kid feels trapped in math practice the whole thing breaks and you'll never get them back.

What surprised me

The piece I did not expect was the diagnostic value of the three second cutoff. Session percentage hides the difference between a fact a kid actually retrieves and a fact a kid is reconstructing each time, those two things look identical on paper because they both produce the right answer, but they are completely different from a working memory standpoint and the kid who is reconstructing every fact will hit a wall the moment the problem gets multi step.

The threshold separates them. You can see exactly which facts the kid has and which ones she's faking. That's the actual signal. Everything else is noise.

What the dashboard shows

The stats page surfaces the top 10 most missed facts for each learner, with average response time and times seen on each one. Free tier shows the number one missed fact, the upgrade unlocks the rest. The average response time column is the one that surprises parents most. You can have a fact at 80 percent accuracy but with a six second average response time, which means the kid is still reconstructing every time and the fact is going to break under multi step problems. The list orders by a blended weakness score, not raw error count, so what surfaces is the actual cognitive load driver and not just whichever fact got missed most often last week.

What I built it with

Vite plus React 19 plus TypeScript on the frontend. Material UI for components, Framer Motion for animations, Konva for the scene builder canvas. The backend is Firebase: Firestore for state, Firebase Auth for the sign in paths (anonymous, Google, email link, plus a learner profile PIN flow I built for kids who shouldn't have their own email yet), Cloud Functions in Node 22 for fact provisioning and lifecycle stuff, Firebase Storage for the scene assets. Stripe Checkout for billing, Postmark for transactional email.

The scheduler is time driven, not session count driven. That matters because a kid who blasts through a session getting easy facts fast shouldn't be promoting facts she hasn't actually consolidated. Each session is built from due cards first, then active learning cards (box 3 or below), then new unseen cards. Cards that hit box 4 or above during a session drop out of the active queue so they don't keep getting tested while she's tired.

Where it is now

I am not running pilots. The app has no users to speak of yet except for my daughter. My mom is a teacher, my daughter's third grade teacher is the first person I've actually shown it to outside the family. I have a free tier for everyone and a separate offer of full access for any teacher who wnats to try it with a class, because what I need right now is feedback from real teachers, not signups.

If you have a kid in elementary or you teach elementary math, the site is at https://mathbuilders.com and I'd take any feedback you have, even harsh ones, especially harsh ones honestly.

Thanks for reading.