So many of the same thing - proportional reasoning in elementary math
Students can start learning proportional reasoning in 4th grade (or earlier) with the help of ratio tables. I don't call them that in this video though, but that's what we are doing: first filling in these tables that show values for two quantities that vary proportionally, and then later using these tables to help us solve word problems. I don't use this type of language in the actual lesson though, so as to not confuse the students. The idea is very simple and accessible to anyone!
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See also
Two-digit multiplication and why we add a zero on the 2nd line
Math Mammoth Grade 4 curriculum