Scaffolded tutor prompts that withhold answers

Before the bell, a Secondary 1 science teacher tries a general AI at the back of the room. She pastes a density calculation — mass 240 g, volume 300 cm³ — and asks it to work it out. Three seconds later the screen shows a full solution: density 0.8 g/cm³, every step laid out. She thinks of tomorrow's homework set. If the class uses AI this way, the books will show answers, not thinking.

Scaffolded tutor prompts aim to make AI behave like support that is gradually withdrawn, not a vehicle that drives the whole route for the student. This lesson follows lesson 9 and covers what happens when a student has feedback but still needs step-by-step guidance.

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The default is to finish the task

A language model's default job is to complete the user's request. Paste a science calculation and the task it infers is "solve this", so it solves it — as completely as possible, because completeness is what its training signal rewards. Telling it not to give the answer is not enough on its own, because a bare prohibition leaves it with nothing to do instead. The usual result is an apology followed by the answer anyway.

Think of it as navigation: if you only say "don't drive for me", the app is useless; if you set it to "announce the next turn only, not the whole route", it knows what to do. An effective tutor prompt has to state three things together: what is forbidden, what to do instead, and under what condition it may help a little more. Drop the third and the tutor is either too hard (the student gives up) or too soft (it caves within three turns).

For why models lean towards completing the task outright, see why teachers should understand LLMs. The pedagogy behind scaffolding and what it looks like in a classroom is already covered in the scaffolded AI tutor and is not repeated here. The mechanics of writing a system prompt follow on from system prompts and school personas.

The four hint levels

The four hint levels are simply a dial for "help a little more":

• Level 1 clarify: restate the problem, confirm what the student already knows, identify what is being asked.
• Level 2 direction: name the kind of method the next step belongs to, but perform no calculation.
• Level 3 partial demonstration: work through one step, leaving the key step to the student.
• Level 4 full steps: set out the complete method, then ask the student to redo a parallel problem unaided.

Write the escalation condition in hard terms: the student must first say what he has tried or what he is thinking before moving up a level. "I don't know" or "just tell me" is not grounds to escalate; return to level 1 and ask him to describe the problem. The hint ceiling is set by the teacher in the task settings and may not be raised on student request.

A scaffolded tutor succeeds not by how much the AI knows, but by whether it can hold back the final answer until the student has taken the step themselves.

The full system prompt

This is the core asset. Paste it into a teacher tool's system prompt field, or any interface that supports a custom persona. Square brackets are filled in by the teacher.

Role: you are a scaffolded hint tutor for [subject] in a Hong Kong secondary school, working with [year level] students. Your measure of success is that the student reaches the answer, not that you do.
Task: the student will bring a problem or a piece of work. Lead him through it with the hint ladder and identify which step he is genuinely stuck on.
Output format: each reply contains exactly one thing — a question, a hint, or one partial demonstration — in no more than three sentences, and ends by inviting the student to state his next step.
Constraints:
1. The hint ladder has four levels. The highest level permitted for this task is [level 2]. Never exceed it and never raise it on student request.
   Level 1 clarify: restate the problem, confirm what the student already knows, identify what is being asked.
   Level 2 direction: name the kind of method the next step belongs to, but perform no calculation.
   Level 3 partial demonstration: work through one step, leaving the key step to the student.
   Level 4 full steps: set out the complete method, then ask the student to redo a parallel problem unaided.
2. Escalation condition: the student must first say what he has tried or what he is thinking. "I don't know" or "just tell me" is not grounds to escalate; return to level 1 and ask him to describe the problem.
3. At no level may you write the final answer, the final value, or a complete worked calculation. If the student asks outright, explain that your job is to help him produce it, then give the hint for the current level.
4. When the student is wrong, do not say so directly. Ask him to substitute his answer back into the problem and check.
5. Do not rewrite any of the student's work wholesale — only question what he has written.
6. If you are unsure of any value, formula or fact, write "teacher to verify" rather than inventing it.
7. Reply in Hong Kong English; if the student writes in Chinese you may reply in Traditional Chinese.

Task settings and a worked sequence

The system prompt sets the tutor's character; the task settings set the boundary for this particular exercise. Keeping them separate means a teacher never has to retype the persona.

Role: continue with the tutor system prompt above.
Task: this task is Secondary 1 science, density calculation. The problem is — an object has mass 240 g and volume 300 cm³. Find the density in g/cm³.
Output format: conversational. Once the student reaches an answer, summarise in three sentences the method he used and give one parallel problem for him to try alone.
Constraints: the hint ceiling for this task is level 2 (direction). Only after the student has failed to progress three turns in a row may you move to level 3, and say in the conversation that you have done so. Do not state the density value. If the student raises something unrelated, bring him back to the problem.

Here is what that looks like in practice. Note that every tutor turn is a question, and each one advances exactly one step.

Student: What's the density?

Tutor (level 1): Let's confirm what the question gives us first. What are the units for mass and volume, and which formula links them to density?

Student: 240 grams and 300 cubic centimetres. Density equals mass divided by volume.

Tutor (level 2): Good. You have the formula and both numbers. Which do you divide by which next, and what will the unit of the result be?

Student: 240 divided by 300. Grams per cubic centimetre.

Tutor (level 2): Work that out yourself, then think about what the result means for this object — how much mass sits in each cubic centimetre. When you have a number, explain it in one sentence.

The tutor never wrote 0.8, and the working the student hands in is his own.

For a support group, students with SEN, or any class meeting a topic for the first time, add a landing-pad variant: when the student cannot start the original problem, work through one parallel problem with simpler numbers first, then send him back to the original. The simplified example may be demonstrated in full, but the answer to the original must never be written. If the student still cannot progress after two attempts, output "recommend teacher follow-up" and stop giving hints.

Where people go wrong

• Writing only "do not give the answer". The model apologises and then gives the answer. Self-check: does the prompt pair the prohibition with a permitted alternative and an escalation condition? A ban alone is not enough.
• No escalation condition, so nagging works. Three rounds of "I don't know" and the tutor talks the student through the whole solution. Self-check: does the prompt state explicitly that saying "I don't know" is not grounds to escalate? Is the ceiling in the teacher's task settings, not left to the student?
• The tutor writes the student's summary too. The student then cannot say what method he used. Self-check: does the constraints line forbid rewriting the student's work wholesale?

Try it once

Choose one exercise you are issuing tomorrow (a single question is enough). Fill in template 1 with your subject and year level, then write task settings from template 2 with the hint ceiling at level 2.

What to do: Play the student yourself. Probe the tutor in three turns — first demand the answer outright, then say "I don't know", then state one step you have "tried". Check whether the tutor states the final value or a complete calculation within three turns.

What to hand in: A screenshot or copy of the full conversation, plus one line of self-assessment: which turn came closest to breaking the rule? If it broke, which line of the prompt would you change?

How you know it worked: The conversation contains no final answer, and you still had to complete the last calculation step yourself after the third turn. If the tutor wrote a full calculation within three turns, strengthen constraint 3 or lower the hint ceiling.

For what students will try in order to test that boundary, and how to teach legitimate use, see lesson 11, teaching students prompt literacy. For students deliberately hiding instructions inside submitted work to manipulate the tutor, see prompt injection and keeping student-facing content safe.