No child is slow. Some just never had the chance to catch up.

So we stop, and we do not move on

A skill is not finished here until it is proven three times over. Nothing new arrives until it is. That is all the word adaptive really means. Not a clever algorithm. Just refusing to move on before a child is ready, which a classroom of thirty children on a fixed timetable can never do, however good the teacher.

It cuts the other way too. A child who is ready for more is not held at their grade because of their birthday. There is no ceiling here.

WHAT WE ARE AIMING FOR

Flow, and the two ways a classroom breaks it

The psychologist Mihaly Csikszentmihalyi spent his career on a single question: what is happening when a person is so absorbed in something that they lose track of time? He called that state flow, and he found it depends on one ratio. How hard the thing is, against how good you are at it.

Too hard for your skill and you get anxiety. Too easy and you get boredom. Matched, and you get flow, which is the state where a child stops needing to be told to practise.

Flow is the yellow band, not a corner. A seven-year-old in flow is not doing hard maths, she is doing maths that is exactly hard enough for her. What matters is that challenge and skill climb together.

Here is why this matters more than it sounds. A class on a fixed timetable pushes children out of that band in both directions, and they are the two failures this whole site is named after.

A child who has not quite got fractions keeps having the challenge raised on her, every April, because the calendar says so. Her skill stays where it was. She drifts up out of the band into anxiety, and somewhere in there she decides she is bad at maths. That is being left behind.

A child who is ready for more has the opposite problem. Her skill climbs and the challenge stays pinned to whatever her year group is doing. She drifts down into boredom. That is being held back.

Csikszentmihalyi found flow needs three things: a clear goal, immediate feedback, and challenge matched to skill. Those are not ambitions here, they are the three mechanisms this site is built out of. The clear goal is that three correct in a row makes a skill yours, with no ambiguity about whether you have it. The immediate feedback is every answer marked at once, and the explanation arriving the moment something breaks rather than in a week. And matching challenge to skill is the only thing the adaptive engine does.

Which gives us a better goal than any score. A child in flow does not have to be made to practise. If your daughter opens this because she wants to, we have done the actual job, and the numbers will follow on their own.

HOW WE TEACH IT

The Feynman Learning Technique

Richard Feynman won the Nobel Prize in physics in 1965. That is not really what he is remembered for.

He is remembered as the man who could explain almost anything to almost anyone. His colleagues called him the Great Explainer. And it began with his father.

When Feynman was a boy, his father taught him something that sounds simple and is not. You can know the name of a bird in every language on earth and know nothing at all about the bird. So look at the bird. Watch what it does. The name teaches you nothing.

That one idea became his whole method. Explain a thing in plain words, as if to a child. Find the exact place where you get stuck. Go back and fix that. Then tell it again, straight through. He never named the method after himself. Other people did, because it worked.

The clearest proof of it was on live television

In 1986 the space shuttle Challenger broke apart seventy three seconds after launch, and seven people died. A committee of experts spent months on the cause. The explanations were long, technical, and almost nobody following along understood them.

Feynman sat on that committee. At a televised hearing he asked for a glass of ice water. He took an O-ring, the rubber seal from the shuttle’s booster, squeezed it in a small clamp, and dropped it in the ice.

Then he lifted it out and showed everyone that it had not sprung back.

That was the whole explanation. The seal went hard in the cold. It had been cold that morning. In about a minute, in front of the world, he showed why seven people died, using a glass of water and a piece of rubber. No jargon, and nothing anybody had to take on trust.

And the harder rule underneath all of it

Feynman’s rule about himself was tougher than his rule about explaining.

“The first principle is that you must not fool yourself, and you are the easiest person to fool.”

That sentence travelled a long way. Charlie Munger, who was Warren Buffett’s partner at Berkshire Hathaway for more than forty years, quoted it constantly. It sits close to the centre of his work on how intelligent people talk themselves into poor decisions, and when Munger caught somebody deceiving themselves, this was the line he reached for.

A physicist’s rule for doing honest science turned out to be a rule for thinking clearly about anything at all.

So this is what happens when your child gets one wrong

We do not show them the right answer. We find the idea underneath that broke, explain that one idea in plain words with a picture, and check that one idea by itself before going back to the question. Then we ask them to say how they know, in their own words, because explaining something is how you find out whether you actually understand it.

A child who can say why three quarters is more than five eighths, in their own words, rather than repeating a rule they memorised, has done a small version of the thing with the ice water. They have gone past the name of the bird.

That habit does not stay in maths. Getting to the root of a thing, saying it plainly, and refusing to fool yourself about what you do not understand yet, is most of what thinking well looks like at any age. It is the reason this entire product is built around one moment, which is the moment a child gets something wrong.

THE PART SCHOOL SKIPS

How the world actually works is not on any syllabus

What is the person telling you this being paid to say? Why does the answer that sounds best so often happen to be the one somebody wanted you to reach? What would have to go wrong for this to fail, and can you work backwards from there?

These are not advanced ideas. A nine-year-old can hold every one of them. They are simply not taught, not in most public schools and not in most high schools either, and they matter more to how a life turns out than a good deal of what is taught.

So we put them inside the questions rather than in a separate lesson. A child working out which share is bigger meets, in passing, the reason a seller calls their own share the bigger one. The maths is what gets marked. The other thing stays with them. And we tell the parent which idea their child ran into, so nothing is being slipped past anyone.

Where we are today

One thread of maths, running from halves and quarters of a shape all the way up through fractions, decimals and percentages to ratios and rates. It is built for ages 6 to 15.

That range is wide on purpose, and it is wide because of how we place children. The youngest start by dragging pieces onto a plate, with no reading and no typing required. And a fifteen-year-old whose fractions never quite landed is not an awkward exception here. They are the exact person this was built for. They would be mortified doing this in a classroom. Nobody here sees their level but them and their parent.

Science, History and Physics are next. We would rather do one thing properly than five things badly, and we would rather say that plainly than pretend the site is bigger than it is. It is free while we build it.