When you set a due date on a lesson, you can also choose to lock it once that date passes - handy for keeping submitted work as-is for marking.
How to lock a lesson after its due date
- Navigate to your class page and open the topic you are teaching.
- Set a due date for the lesson by clicking the calendar icon.
- Turn on the Lock after due toggle for that lesson.

What students see
Once the due date passes, the lesson becomes view-only for your students. They can still open the lesson and review their work, but no more changes can be made. Students see a lock icon beside the lesson explaining that editing has closed.
You can turn the toggle off at any time to reopen editing - for example to give a student an extension.