Roles that help, and roles that do nothing

What a role actually does

“You are an experienced examiner for a national science board.” Put that at the top of a prompt and the output changes: shorter stems, precise command words, mark allocations, a certain dryness. Why? Not because the model has become an examiner. Because the model has read a great deal of text written by examiners (mark schemes, examiner reports, specimen papers) and the role words pull its predictions toward that body of writing.

That is the whole mechanism, and it tells you which roles work. A role helps when the people who hold it write in a way that is distinctive and well represented in the training text. A role does nothing when it is a compliment.

Roles that do nothing

• “You are a world-class expert.” Experts do not write with a label saying so. There is no distinctive expert register to steer toward; you get the default with more confidence.
• “You are a genius teacher.” Same.
• “You are the best copywriter in the world.” Same, and it tends to add hype.
• “You are helpful and accurate.” The model is already trained to try to be; saying it changes nothing.

These are the roles that fill prompt-sharing websites and they are decoration. If you have been using them, drop them and you will lose nothing.

Roles that earn their place in a teacher’s prompts

The examiner. Produces questions with command words, marks and a scheme. Name the board if it is well known; the model has read its examiner reports.

The confused student. “You are a Class 9 student who has just learned this and has one common misunderstanding. Answer this question the way that student would.” This is the most useful role in teaching. It gives you a preview of wrong answers before you see them in a pile of scripts, and the wrong answers it produces are realistic because the model has read thousands of student misconceptions in teaching forums and research papers. Ask for three different confused students and you have three misconceptions to plan around.

The sceptical parent. “You are a parent who thinks this homework is pointless. Ask me the questions you would ask at a parents’ evening.” Rehearsal for a real conversation, and the questions are sharper than you expect.

The textbook author. “Write this the way a school textbook for this age would” produces a more structured, more neutral explanation than the default chat voice.

The colleague who disagrees. “Give me the strongest argument that this lesson design will fail.” Useful before you commit an hour to a plan.

The subject specialist, named specifically. “A geography teacher” does more than “an expert”, because geography teachers have a distinctive way of writing about causes, scales and case studies.

Roles for students, not just for you

A role is also a way to let a student use the tool without it doing the work. “You are a tutor who never gives the answer. Ask me one question at a time to help me find it myself.” This is the shape of a Socratic tutor and it works reasonably well, with a caveat covered later in the course: models want to help, and “never give the answer” erodes over a long conversation. Reinstate it every few turns.

Roles versus the five things

A role is not a substitute for the five things only you know. “You are an experienced Class 5 maths teacher” is a role; it does not tell the model your class believes 1/3 is smaller than 1/4. Use the role to set the register and the five things to set the content. Both, in that order, in the same prompt.

Checking that a role did anything

Run the prompt with and without the role. If the two outputs are indistinguishable, the role is decoration and you can stop typing it. Teachers who do this once find that about half the roles they had been using do nothing, and two or three do a great deal. Keep the two or three.

The honest limit

A role can pull the model toward a register it should not be in. “You are a doctor” produces confident medical writing regardless of accuracy, and “you are a lawyer” produces confident legal writing that may be wrong for your country. The confidence comes from the role; the correctness does not. For a school this matters most with safeguarding, medical and legal questions, where the right role is no role at all and the right action is to ask a person.