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Q. In “People in chef’s coats were being shepherded from room to room,” should it be written as “chef’s coats,” “chefs coats,” or “chefs’ coats”? I’m guessing that it’s the former, since it is a single, standardized coat that all the chefs are wearing, but I’m not sure.
A. You are correct: the plural of “chef’s coat” is “chef’s coats.” There are a bunch of nouns like that one. For example,
batter’s box (sing.), batter’s boxes (pl.)
buyer’s or seller’s market (sing.), buyer’s or seller’s markets (pl.)
lady’s slipper (sing.), lady’s slippers (pl.)
teacher’s pet (sing.), teacher’s pets (pl.)
So, for example, you might refer to a teacher’s pet in one classroom or to several teacher’s pets in one or more classrooms.
But if, instead of model students, you were referring to two or more teachers and their cats or dogs (or other such animals), you’d write “teachers’ pets” (note the placement of the apostrophe).