Sooner or later the practice page shows you a question you are sure you have seen before. Maybe you got it right the first time. Maybe it feels too easy to bother with. It is there on purpose, and on a date chosen for you.
That date comes from your answers, and you can follow how it is worked out without any maths. Once you see it, an easy question coming back makes sense, and so does the best way to spend the few minutes a day that keep what you have learned.
How forgetting works
Forgetting is not a slow, even leak. You lose a lot in the first days after learning something, then less and less as time goes on. Drawn as a graph, it is a steep slope that flattens out, and it has a name: the forgetting curve.
The useful part is what happens when you pull a memory back out. Each time you recall something, especially when it takes a little effort, the slope after it becomes gentler. The next time, it takes longer to fade. Recall it again, and it lasts longer still. A fact you have recalled four or five times, at growing gaps, can stay with you for months without any further work.
Rereading does not have the same effect. Seeing the answer again feels like knowing it, but nothing was pulled out of memory, so the curve stays almost as steep as before. That is why the school asks questions rather than showing you the lesson again.
Review just before you would forget
If recalling a memory makes it last, the timing of the next attempt matters a lot.
Review too soon and it is wasted effort: the answer is still right at the front of your mind, so recalling it does very little. Review too late and the memory is gone; you are learning it from scratch. The sweet spot is in between, when you can still get the answer but have to reach for it a little. That small strain is what makes the memory stronger.
Nobody can feel that moment for themselves, and it is different for every question. A rule that is easy for you may be slippery for someone else, and the reverse. So the school keeps track for you.
What happens to a question after you answer it
Every question you answer, in a lesson quiz or on the practice page, becomes a card in a spaced repetition system: a schedule that brings each card back at growing intervals. The school uses an algorithm called FSRS (Free Spaced Repetition Scheduler) to set those intervals. For each card it estimates how likely you are to remember the answer on any given day, and it books the next review for the day that chance drops to about nine in ten. That is the "just before you forget" moment, worked out per question.
Your answer moves the date:
- A right answer pushes the next review further out. The gap grows each time. If you answer a question right every time it comes due, it returns after ten minutes, then after about two days, then about eleven, then about six and a half weeks, then about five months.
- A wrong answer brings it back soon. The card starts again with short gaps, and they grow more carefully than the first time, because the algorithm has learned that this one slips.
So a question you keep getting right soon becomes rare. A question you keep missing stays close until it sticks.
All of this lives in your browser, on your device. There are no accounts, and nothing you type in a lesson or a quiz leaves your browser unless you switch on the AI instructor in the settings.
How the daily mix is picked
Today's mix, at the top of the practice page, is five questions chosen by fixed rules, in this order of priority:
- Cards that are due, meaning their booked review date has arrived.
- Questions you got wrong the last time you saw them.
- Questions from lessons where you are weakest, and from finished lessons where most of your recent answers were wrong.
Two more rules shape the five. Once you have started some lessons, the mix only draws on those, so it does not quiz you on material you have not met yet. And it takes at most two questions from any one lesson, so a single tricky lesson cannot fill your whole session. Each question shows a short label saying why it was chosen, such as "Due for review" or "Missed last time", followed by the lesson it comes from.
Why an easy question still comes back
There are three reasons, and none of them is a mistake.
First, easy is not the same as permanent. A question can feel obvious today because you saw it recently. The schedule cares whether you can still answer it after a long gap, and the only way to find out is to ask. It books the review for a day when you still have about a nine in ten chance of getting it right, so most reviews are meant to go well. When one feels easy, that usually means the timing was early enough to keep it alive, which is the point.
Second, the school records only two outcomes: right or wrong. It does not ask how hard the question felt, so a right answer you produced instantly counts the same as one you had to work for. Either way the gap grows, and an easy question that keeps coming back right will soon be months away.
Third, the mix has five places to fill. On a day when fewer than five cards are due and you have no recent misses, the remaining places go to other questions from lessons you have touched, labelled "Keeps it fresh".
Lesson quizzes bring old questions back too: one of their three questions comes from an earlier lesson that the current one builds on, so earlier ideas keep being used while you move forward.
Why there is no "I know this" button
You cannot mark a question as known and remove it from your reviews. That is deliberate.
The feeling of knowing something is a poor guide to whether you will remember it in a month. It is strongest right after you have read the answer, which is exactly when it is least reliable. A button would let that feeling decide, and the questions you skipped would be the ones that quietly disappear.
The only way to move a question out of the way is to answer it. That costs a few seconds, and each right answer pushes the next appearance much further away than the last. A question you truly know does not need a button. It needs two or three right answers, and then you will rarely see it.
How to use the daily mix
- Do it first. Before you start a new lesson, run the mix. It takes a few minutes, and new material is easier to learn when the old material it builds on is fresh.
- Keep it short. Five questions is the whole job. You do not need to clear every due card in one sitting; the schedule is built for a little every day.
- Answer before you look anything up. Looking first turns recall into recognition and removes the effect you came for.
- Read the explanation when you miss. That question will be back soon. The explanation is what makes the next attempt a right one.
- Do not worry about missed days. If you skip a few, nothing breaks. The mix still takes five questions, due cards first, and the rest wait for the next day.