Expectations
Philosophy
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This is no blazing piece of insight, but as one of those basic principles of good teaching, you need to communicate expectations clearly.
In the same way that it is OK for you to tell classes now to "Put down pencils. I want all eyes on the front board," it is also OK to tell them that you need "Laptop lids down."
Kids that insist that they are taking notes via the laptop should be required to post them. If you are using Moodle or Blackboard, that is probably pretty easy.
You may have to get the student to send you the notes, but this provides an opportunity to work on note-taking skills. In a math class it would probably be pretty hard to take good notes with the laptop.