Subtraction Help...

Discussion in 'Elementary Education' started by Miss JE, Nov 6, 2011.

  1. Miss JE

    Miss JE Companion

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    Nov 6, 2011

    My third graders cannot subtract and I am lost on which direction I should take them...

    1. Show them the standard algorithm. They all TRY to do this but they don't understand what they are doing so they aren't successful. I could probably get them to be able to subtract by doing this but risk the kids not actually understanding what they are doing...

    or....

    2. Show them multiple strategies. I have shown them several strategies that some are trying and finding a little success. The problem is that it is difficult to plan as there are not really lesson plans for these types of things. I feel like I need to do some direct instruction but have no plan to follow... I also think that they will make better sense of subtraction this way but it may take longer and we just don't have the time.

    Ideas, teach the algorithm or show them other strategies they may connect better with...???
     
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  3. bonneb

    bonneb Fanatic

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    Nov 7, 2011

    I believe it is always best to teach them as many strategies as possible. Most kids land on one and that is what they use.

    For third grade you still need to give them manipulatives - if they are having trouble with subtraction they have some kind of gap. They still need something concrete so they have an understanding of what they are doing. With enough use of manipulatives, they WILL "get it" eventually. It might seem like you are "wasting time," but in the long run it will be of great benefit to them.

    And don't forget to include any and all addition/subtraction games, including the old fashioned kind, teacher-created, and computer games. Hit them from all sides!
     
  4. Aliceacc

    Aliceacc Multitudinous

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    Nov 7, 2011

    It sounds to me as though you need to go back and reteach place value. Once you understand that that 5 really represents 5 tens, it makes a whole lot more sense to convert one of those tens into ten ones.

    Cutesy strategies don't get to the core of the issue-- that the subtraction algorithm is all about place value. Then later, when kids NEED to know place value again, they're still stuck.
     
  5. DizneeTeachR

    DizneeTeachR Virtuoso

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    Nov 7, 2011

    When teaching place value I like to use tally marks and "convert" them to the numbers.

    I make my own sheet of pictures, they tally mark them, circle groups of ten to put in the tens place and what is left over goes into the ones place.

    I think showing them different ways to subtract is key as well. I know when I started teaching addition & subtration to my 1st graders I would show them one way & ask the students if they did it a different way. Sometimes 2-3 students would come up. I always told them "Math is finding the "trick" that works for you." I firmly believe that.
     
  6. **Mrs.A**

    **Mrs.A** Comrade

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    Nov 7, 2011

    I had a couple of fourth graders who were still having a hard time with subtraction this year...I used the noun/adjective method and they really seemed to get it. This is how I had them set up the problems...

    4 hundreds 2 tens 6 ones
    - 2 hundreds 4 tens 8 ones
    _____________________________

    Of course, everything should line up... I had them do all the regrouping before they started to subtract. It really seemed to help.
     
  7. Aliceacc

    Aliceacc Multitudinous

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    Nov 7, 2011

    That's brilliant!!!
     
  8. amakaye

    amakaye Enthusiast

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    Nov 7, 2011

    Paper money has worked well for some of mine (only using 1s, 10s, and 100s)--tell them the cashier doesn't have any change, but they can make exchanges at the bank. Have them record how many of each bill they have at each step (maybe with a place value chart?). They seem to quickly get that they can't give the cashier 7 ones if they only have 4. Or, do you have access to base ten blocks? We work a lot with those before doing the standard algorithm. We practice with the actual blocks, then transition to drawing the blocks and our regroupings.

    We also draw a lot of pictures and make them into story problems. If we're doing 85-27, we'll talk about having donuts in boxes of ten (8 full boxes and 5 extras), and how your little sister ate 27 (two full boxes and 7 extras), so she must have opened up a box of ten...

    If you have any that struggle with keeping things lined up, I've found that having them turn their paper sideways so the lines can be columns for each place really helps.
     
  9. DizneeTeachR

    DizneeTeachR Virtuoso

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    Nov 7, 2011

    Ama... like changing the paper directions.
    Graph paper works well.
     
  10. amakaye

    amakaye Enthusiast

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    Nov 7, 2011

    Yeah, I've used graph paper before, but the only stuff I could get my hands on this year was a bit too small (especially for a couple of my sloppy writers, who were the ones needing help keeping things lined up!).

    MissJE, do you have a math curriculum you are following?
     

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