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> There is a vast difference between “never learned the skill,” and “forgot the skill from lack of use.”

This sentence contains the entire point, and the easiest way to get there, as with many, many things, is to ask “why?”

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Most people learn multiplication by memorizing a series of cards 2x2,2x3.. 9x9. Later this gets broken down to addition in higher grades.
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Most people learn multiplication by counting, it has been in basic mathbooks since forever. "1 box has 4 cookies. Jenny ha 4 boxes of cookies. How many cookies do Jenny have?" and so on, the kids solve that by counting 4 cookies in every of the 4 boxes and reaching 16. Only later do you learn those tables.
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That’s definitely not how I learned it, nor how my kids have learned it. I vividly remember writing out “2 x 3 = 2 + 2 + 2 = 3 + 3.” I later memorized the multiplication table up to 12, yes, but that was not a replacement of understanding what multiplication was
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