Subtraction Within 20 – The Cost of Working Memory

Part of our role as educators is to continually reflect on the teaching methods and evolve them as we adjust to students’ learning. One such adjustment came about from teaching our first graders addition and subtraction for numbers within 20. Specifically, the problem of subtraction with regrouping was a major hurdle the kids had to get through. Let us look at some examples from the textbooks and workbooks, and why we decide to tweak the method for our classes.

Remainder 6 or 60?

…the tricky part came in when there was a remainder. In Question 2, 630 divided by 60.
Student A: “By following the previous example, we know that 630 divided by 60 is the same as 63 divided by 6. Ten 6s goes into 60, which gives a remainder of 3. The answer is 10 R 3.“
Student B: “No. Ten 60 goes into 600, so the remainder should be 30, not 3!”
Why is there a difference?…

Squares and Triangles

One day after class, a parent came to me and ask about a question he saw in one of the challenging questions I gave to the students. He said he would (as would many adults) solve this using simultaneous equations (or System of linear Equations) but would like to know how to teach his kid in 3rd grade without the use of algebra. I invited him to stay for a while to observe the next class. Students were given Think-Pair-Share to solve that particular question and after minutes of work time, a student raised her hand and this is what she came up with.

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