Half the essays sound the same
Do not start with a detector or an accusation. For the next essay, have students write their thesis and first paragraph by hand in class, tie the prompt to something only your class has seen, and collect two lines on what changed between the attempt and the final. You will get different essays, and you will have something fair to talk about when you do not.
What is going on
The same three-part structure. The same balanced conclusion. The same handful of phrases. You are probably right about where it comes from, and you still cannot prove it for any one student.
Sameness is a known effect and it does not need bad intent. In an experiment with 293 writers (Doshi and Hauser, Science Advances, 2024, peer reviewed), stories written with AI ideas were rated more creative one by one and were more similar to each other than stories written without. Those were short stories by adult writers, not school essays, but the pattern matches what you are seeing. A student who only asked for "some ideas" can end up in the same place as thirty others.
What to do this week
Start the next essay in the room
Ten minutes, on paper: a thesis sentence and a first paragraph. Collect it or have students photograph it. The final essay must grow from that start.
Anchor the prompt
Ask for one link to something a chatbot has not seen: Tuesday's class discussion, a local example, a passage you chose, the student's own experience.
Ask for "what changed"
Two lines with the final: what I changed from my first attempt, and why. Mark it as done or not done.
Talk, do not accuse
Where an essay still worries you, ask for two minutes: "Walk me through your argument." Most cases resolve themselves in that conversation, one way or the other.
What not to do
- Do not treat a detector score as proof. It is not proof either way, and honest students get flagged.
- Do not punish the batch you already have on suspicion alone. Change the next assignment.
- Do not ban "AI for ideas" without replacing it. Give students a way to find their own first idea, which is what the in-class start does.
The honest limit
A determined student can still get round all of this. The aim is not to make copying impossible. It is to put the marks where the student's own thinking shows, and to give honest students an easy way to show it. Follow your school's policy on what you may require.
Questions
Does similar wording prove students used AI?
No. Students also share phrases from the same textbook, the same revision site and each other. Similarity is a reason to look at the process, not a finding.
What about longer take-home essays?
Ask students to draft somewhere that keeps a history and to be ready to walk you through it. Our free writing pad records on the student's own device how a draft was produced. It is not a detector and does not prove identity.
How much extra marking is this?
A little. The in-class start takes ten minutes of lesson time, and "what changed" needs reading only when the final essay raises a question.