From: Jeanne (for Teacher2Teacher Service)
Date: Jan 14, 2006 at 23:48:53
Subject: Re: Modeling Subtraction of Integers using Red and Yellow Counters

Hi Mimi,

I use a manipulative called "tile spacers" to help me teach addition and
subtraction of integers. They are shaped like plus signs and can be
purchased from a home improvement store that sells ceramic tiles. To make
negative signs just take a pair of scissors and snip two "legs" off.  These
have the advantage of looking like "+" and "-" signs.  I am not saying that
you should go out and purchase these items, but these manipulatives remove
at least one level of interpretation and for some struggling students this
makes a big difference.  Before I discovered tiles spacers I used tiles to
teach this concept and had my students write "+" on one side of the tiles
and a "-" on the other.

Anyway, I begin by showing my students that a "+" and a "-" make a zero and
that "++" and "--" make zero and that "+++" and "---" make zero...etc.

We start each problem with some zeros on their work space. I call
them "zeros" and not "a plus and a minus." I take advantage of their
understanding that adding zeros does not change the value of a situation.

Example:  3 - -4  "3 minus -4"   This means we put in 3 and we TAKE OUT -4

  -------------       -------------        -------------
 | +++++       |     | +++++  +++  |      | +++++  +++  |
 | -----       | --->| -----       |  --->| -           | ---> Value = 7
 |             |     |             |      |             |
  -------------       -------------        -------------
   Value = 0           Put in 3              Take out -4


Hope this helps!

 -Jeanne, for the T2T service

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