Shhhhhhh.
This is an easy one. There are times every day when the classroom needs to be quiet and the students have focused time to do their work, read, write, etc. I have found this to be most profitable to the students directly after a lesson. I remember as a student learning a new concept, and then having some time in class right after I had learned it to practice it. This really helped "cement" the concept into my brain, and I valued that time.
With younger students, it is nice to have a fifteen minute silent reading time. I have often let my students choose any book in my room that they want to read and just let them enjoy reading. Other times I would have them read a chapter book.
The toughest part about quiet time for a teacher is to keep all the students quiet and focused. The classroom culture has a lot to do with this. Have expectations and enforce them. We teachers need to make the environment conducive to quiet working or studying. It's our responsibility.
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