How to Teach Subtraction - ProTeacher Community


JBL
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JBL
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How to Teach Subtraction
Old 02-11-2006, 01:52 PM
 
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I haven't been student teaching for very long, but it's been long enough to watch my co-op teaching the students (2nd graders) how to do two-digit addition. I learned about the little squares (ones) which get regrouped when you have 10 of them so that you end up putting one ten-piece in the tens column to take their place. It hasn't been too confusing to understand, but it's been very confusing to imagine how to teach it myself.

My co-op will soon be finished with addition. Then it's on to two-digit subtraction, and it will be my turn to teach! I'm very nervous about this because I don't want to instill the wrong things in the minds of these young children, with regards to the regrouping process (which I really don't understand how it works backwards). I will have a book to follow, although my co-op doesn't like to offer too much help because she wants to see what I can do on my own.

This is really easy for her because she's been teaching it for 28 years! I, on the other hand, have never taught it. I would much rather teach geometry, measuring, time, money, numerical patterns, bar graphs... virtually anything except subtraction. Does anybody have any advice on how NOT to mess this important concept up for the kids?


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donna
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start slow
Old 02-11-2006, 03:03 PM
 
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I am also moving on to 2 digit subtraction this week. My advice would be to start slowly. This can be a difficult concept so don't try to do too much too fast. I like to start by teaching a regrouping game using workmats and base ten blocks. Then the next day I may move on to the subtraction lesson.

The Banking Game
(model this on the rug in a circle with another student for everyone to learn)
Partners each have a workmat divided into hundreds, tens and ones sections and use base ten blocks and a die to go from 100 to 0.
Partners start with a hundred flat on their workmat. They roll the die and need to take that amount off their board. If they roll a 4 for example they will need to trade in the hundred for 10 tens, then trade 1 ten in for 10 ones and then take 4 away from the ones. They will need to regroup when necessary for their next turn. The first player to make it to zero wins.

Subtraction Lesson
When I formally teach subtraction with regrouping I always start with just the tens and ones workmat and the base ten blocks. (No paper and pencil stuff yet.) It helps to model it on an overhead along with the kids, so the kids that may be lost can follow along with you.

I would start by asking them to show me 25, for example, on their workmat (2 tens and 5 ones). Next I would have them take away 4. Where will you take them from? (the ones side) The first couple of examples would not require regrouping.

Next I would move on to problems that require regrouping.
Show 34 on your workmat. (3 tens and 4 ones)
Now take away 6. (there will not be enough ones to do that)
Where can we get more ones? (from the tens side)
Take a tens rod and trade it in for 10 ones and put them on the ones side. Now take the last 2 ones to make minus 6.

Good Luck!
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Brooke S. Brooke S. is offline
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Brooke S.
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subtraction
Old 02-11-2006, 08:50 PM
 
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It is a hard concept for them to understand. After moving on from the manipulatives to the pencil/paper this is how I do it.

Problem: 57
-29
-----

I would say: "Can we do 7 take away 9?" If I have 7 apples could I give you 9 of them?

Kids say: No

I say then we have to regroup. I'm going to go up to my next door neighbor and say " Mr. 5 will you please give me 1 number? Mr. 5 says sure.. Then I cross out the 5 and write a four.. I put the number he gave me (1) next to the 7.

Then I do the problem. This really helps them because they think it is funny. I can ask them again and again what we have to do and they will say, borrow from Mr. ....

I hope this helps. It is helpful once they get going with the regrouping to throw in some problems that don't need regrouping, because they get confused and forget that they don't need to regroup.
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apple annie apple annie is offline
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apple annie
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Subtraction
Old 02-12-2006, 04:43 AM
 
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I teach subtraction a lot like the above post, saying every time...

Me: Bigger on bottom?
Students: Yes
Me: What do we do?
Students: Borrow from our neighbor!

OR...

Me: Bigger on bottom?
Students: No
Me: It's a NIKE problem?
Students: Just do it!

(Disclaimer... Now that Nike doesn't use that ad campaign so much I have to spend a little time teaching about about advertising slogans first.)

Also, I just wanted to add that before I go to subtraction WITH regrouping, I always spend a day reviewing and give an easy test on subtracting two digit numbers without regrouping. Builds confidence and gives them an easy 100 to offset the potential drop in grade when they approach a new and difficult concept.
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Room22
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substraction
Old 02-24-2006, 09:53 AM
 
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I agree with using manipulatives first and place value activities like the Banking game.

In our school with 11 second grade classrooms, most of us use the saying (0ver and over) :

More on top, no need to stop 39 - 24

The numbers the same, zero's the game: 37-27=

More on the floor,
Go next door and get ten more. 32-19


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mrssimon2nd
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mrssimon2nd
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second grade teacher
Old 03-03-2006, 04:29 PM
 
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I don't remember where I got this but it has worked well for my kiddos!

More on the top
No need to stop

More on the floor
Go next door and get ten ones more!
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miss carreon
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Old 11-07-2007, 06:18 PM
 
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I just went to see Rick Morris at one of his workshops and he mentioned the poem;
More on top,
No need to stop.
More on the floor,
than go next door and ask for ten more!`

I've taught the kids this way the last three days and they love it! teaching regrouping seems much easier now to handle

Good Luck
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