31 percent less time on lesson preparation, with materials of the same quality. That is what a randomised trial in England measured in 2024.
When people talk about AI in schools, it is mostly about exams and homework. Many teachers face a different question on a Sunday evening: how do I get through all this preparation? On that question, there is now a solid measurement.
What the trial measured
In 2024, the Education Endowment Foundation (EEF) ran a trial in England with 259 teachers from 68 schools, evaluated by the research institute NFER. Schools were randomly assigned to two groups. One used ChatGPT for lesson preparation, the other prepared without AI.
The ChatGPT group spent an average of 56.2 instead of 81.5 minutes a week, a little over 25 minutes or 31 percent less. An expert panel rated the materials from both groups without knowing where they came from. It found no difference in quality.
What the trial doesn’t tell you
The trial looked at secondary school science (Years 7 and 8 in the English system), and the teachers had a guide on how to use the tool. Whether the figure carries over to other subjects, other age groups or use without guidance is not something the trial answers.
The three time sinks below don’t come from the trial either. They are my recommendation for where the same idea applies: the AI delivers a draft, and the teacher turns it into something usable.
Course leaders in continuing education can apply this too, for example to course announcements, messages to participants or rubrics for course assignments. The trial did not measure that.
Three time sinks to hand over
- Letters to parents and announcements. The AI writes the first draft, you adjust tone and content.
- Differentiation. The same task at three levels of difficulty, or a text in plain language.
- Grading rubrics. The AI suggests criteria and levels, you sharpen them.
The boundary stays clear
The AI delivers drafts, you make the decisions. Whatever goes out is your responsibility.
And personal data stays out. The public schools of the Canton of Zurich make the same point in their guidance on AI. You can draft a letter to parents with placeholders such as “[name]” or “[date]” and fill them in only at the very end.
One week, one time sink
Pick a single time sink for next week, not all three. For differentiation, for example: give the AI a task from your current teaching, without any details about your class, and ask for three versions, an easier one, the original and a more demanding one. Then check: is the content correct? Does the level suit your learners? What would you change?
Make a rough note of how long it would have taken you and how long it took with a draft. After a week you will know from your own experience whether it pays off for you. An average from England can’t tell you that.
Time saved is time for relationships and good feedback.
