Why Billy never gives the answer

The easiest way to build an AI helper for exercises is to let it answer questions directly. It's also the fastest way to make the exercises pointless — a student who can ask for the answer will ask for the answer, especially at 9pm with three more exercises to go.

Billy's guide is built the other way around. When a student gets stuck, it offers a hint or a guiding question — never the answer, never even a strong enough clue that answering it is equivalent to answering the exercise. The policy is embedded directly in the system prompt, not left to the model's judgment on a given request.

This matters more for a tutor than it might seem. A worksheet with answers copied from a hint bot tells you nothing about what a student actually understands. A worksheet completed with only Socratic nudges tells you exactly where they got stuck, because Billy's transcript of that conversation is attached to the attempt — so the tutor sees not just the score, but the path the student took to get there.