Ask ten experienced teachers how long they spend planning a lesson and you'll get ten different answers. Ask ten newly qualified teachers the same question and you'll get numbers two or three times higher. This gap is instructive.
What the research says
UK Department for Education data consistently shows that teachers spend an average of 10–12 hours per week on lesson planning and preparation. For a teacher with a full timetable of 25 taught hours, that's roughly 25 minutes of planning per lesson hour. For a teacher with a heavy planning load across multiple subjects or year groups, it can be significantly higher.
Experienced teachers typically report spending 10–20 minutes planning a lesson they've taught before in a similar form. For a new topic or a new year group, 30–45 minutes is common. For a first lesson ever on a topic — true from-scratch planning — an hour or more isn't unusual.
NQTs often report spending an hour or more per lesson regardless of whether the content is new to them, because the confidence to judge "this is enough planning" takes time to develop.
The diminishing returns of over-planning
There is a point beyond which additional planning time does not produce a better lesson. More detail in the plan does not mean better teaching — it often means the plan becomes a script rather than a guide, and scripts make for stiff lessons.
The most effective lesson plans are the ones that are thorough enough that you can teach from them confidently, but not so detailed that you're reading from them rather than responding to the room. For most experienced teachers, that's a plan they could write in twenty minutes.
Where the time actually goes
Most of a teacher's planning time doesn't go on the thinking — it goes on the production. Formatting the plan, creating resources, finding images, building slides, generating worksheet questions. The intellectual work of deciding what to teach and how to structure it is usually done quickly; the mechanical work of creating the materials takes far longer.
This is precisely where AI tools provide the most value. Generating a vocabulary list, creating ten quiz questions, producing a differentiated version of a task — these are mechanical tasks that AI handles in seconds. The thinking about whether those questions are the right questions, whether the differentiation is appropriate for these specific students, remains with the teacher.
A reasonable target
For a lesson that's been taught before in roughly this form: 10–15 minutes. For a new topic in a familiar subject: 20–30 minutes. For genuinely new-to-you content: 45 minutes, with the expectation that this investment pays dividends when you teach it again.
If you're consistently above these numbers, the question to ask is: what am I spending the extra time on, and is it producing better lessons? For most teachers, the honest answer is no — the extra time is going on anxiety management and perfectionism, not on thinking that improves outcomes.
AI lesson planning tools don't solve the anxiety. But they do remove enough of the mechanical work that the planning time is more likely to land within these ranges, even on difficult weeks.
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