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Q&A #19133


Teaching borrowing in subtraction

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From: Claire (for Teacher2Teacher Service)
Date: Dec 11, 2007 at 00:14:20
Subject: Re: Teaching borrowing in subtraction

Hi, Carolyn --

Thanks for writing to T2T. I think what you really want is the most effective
method, the one that will make the most sense to children and therefore be
remembered.

Make sure the children understand the concept of subtraction -- what it
means, that it's used to find differences between two quantities as well as
to find what remains after a quantity has been removed. Make sure they can
model subtraction without borrowing with diagrams or manipulatives. My
favorite tool for this work is base 10 blocks. If you don't have then in your
classroom, you can use the virtual ones at
http://nlvm.usu.edu/en/nav/frames_asid_155_g_2_t_1.html

Once they have mastered subtraction without borrowing and can model it with
manipulatives, they will understand why they need to do something differently
when borrowing is called for. Teach them to regroup with the blocks, while at
the same time showing them how the steps are recorded on paper.

It's important, whenever teaching a new procedure, to do it in the context of
a problem situation. That helps give meaning to the steps and children will
connect with it more readily. "The pet store had 32 puppies on Monday. During
the week they sold 19 of them. How many were left?"

There are other algorithms (procedures) for subtraction than the traditional
borrowing one taught in the US. Some of your children may make more sense
from an alternate method. You can see some explained at
http://instruction.aaps.k12.mi.us/EM_parent_hdbk/algorithms.html

I do strongly recommend that, with whichever method you use, you don't use
language such as, "We can't subtract a larger number from a smaller one." It
happens all the time, and it's called "debt." ;-) When it's 6 degrees F. in
Vermont, it can indeed get 10 degrees colder.

As children learn new procedures, have them talk their way through it as much
as possible. The language is very important to the learning and it takes lots
of practice to get the words right.

I hope this is helpful. Please write again if you have more questions.

 -Claire, for the T2T service

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