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Is there a preference in the CCSS for naming the size of arrays as “rows by columns” or “columns by rows?”
If you search the CCSS document for the term “array,” you will find one example that involves different numbers of rows and columns: “The apples in the grocery window are in 3 rows and 6 columns. How many apples are in there?” (There are others in the Operations and Algebraic Thinking Progression.) The phrasing used is “3 rows and 6 columns” rather than “3 by 6.” That avoids the need to know whether “3 by 6” means “3 rows and 6 columns” or “6 rows and 3 columns.”
As discussed in the OA Progression (p. 24), seeing one array as a rotation of another (e.g., an array with 3 rows and 6 columns is a rotation of an array with 6 columns and 3 rows) can be used to illustrate the commutative property. So, at some point, students see that e.g., an array with 3 rows and 6 columns has the same number of objects as one with 6 rows and 3 columns.
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