AP Biology · Calc AB · Psychology · Environmental Science
It's not Unit 3. It's four ideas you keep getting wrong.
Most practice hands you a score. Cramfox names the idea underneath the misses — the one you bring to every question that touches it — and gives you the line that fixes it.
A linear polymer is assembled from 12 monomers by dehydration synthesis. How many water molecules are released during its assembly?
Not this time.
Why B tempts youAssumes one water is released per pair of monomers rather than per bond formed.
Water goes with the bond, not the block. Line up n blocks and you get n minus one bonds, and one water each.
What makes it different
Every other app tells you which questions you got wrong. Cramfox tells you which idea you have wrong.
How it works
Aim at the weak spot. Test it. Read the fix.
It aims
The fox re-aims after every answer, so the next question lands where the evidence says you are weakest — not where you left off.
It names
Every wrong choice was authored to express one specific misconception, and its rationale was written before the question was. So a miss can tell you what you were thinking.
It teaches
Behind each named error is 300–500 original words and one line built to survive into the exam room — the thing you actually needed when you got it wrong.
The part nobody else has
Three mistakes, or one idea you hold wrong?
Miss the same idea in three different units and most apps show you three unrelated mistakes. Cramfox shows you one — named, counted, and practisable on its own, pulling questions from every topic where it hides.
It works because every distractor in the bank is tagged to the misconception it expresses. That is authoring work, not a model call — which is why it cannot be retrofitted onto a bank that was not written this way.
Proof that expires
A green square earned in October is a lie by May.
Four levels, each with the rule that moves it written on the screen. Proof has to be confirmed on a later day by a scored test — never by the drill that just showed you the answer — and it fades, because a signal that can go down is the only one worth acting on in April.
Built, not promised
Original questions, written against the current course framework.
original questions live
topics mapped across 4 courses
distractors per question, each tagged to a misconception
College Board questions reproduced, ever
Every unit and topic is read from our machine-readable course outlines, verified against the published frameworks on 2026-07-27 — including the AP Biology Unit 1 reorganisation that took effect for the 2025–26 year.
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Use these without an account.
Real cut points, and a link you can share with the whole group chat.
Every unit, every topic, with exam weightings and sample questions.