I also have students sit wherever they want the first day of class. The ones that can not handle sitting by their friends usually get moved in the first week of school. If they want to sit next to their friends, they learn to control their talking. I change the seating chart every 9 weeks or as needed.
Last year I had a class of 42 7th graders. It was extremely crowded and since it was right after lunch they were a more hyper than usual. My advice is to use a seating chart, call home, and be consistant.
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