How is subtraction taught in grade school these days?
My grandson was struggling in the third grade and I discovered he was taught to go from left to right and to cross out numbers as he went. I found this very cumbersome and inefficient compared to the right-to-left way I learned years ago which involves only carrying "ones" when necessary.
Do present teachers of math actually know the subject or just learn protocols for teaching it by whatever method happens to be fashionable? No wonder Finnish students are 'way ahead of ours.
Aleta L2008-03-20T07:08:26Z
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There is a crisis in education as you have wisely surmised.
"New" but not better techniques are being taught to children for all manner of processes. They are taught meaningless algorithms to get an answer without being taught the underlying principles to support those algorithms.
Help your grandson understand subtraction by getting a cheap set of manipulatives to use. Have him physically "take away" the amounts needed. Then he will be able to understand that if there are not enough in any place value, he will need to exchange one form the next higher place value for ten of the needed place value. Before he continues, help him with the notation that you learned with these simple questions (for example): Do you still have 7 tens? No, only 6, so let's cross out the 7 and write 6 above it. Do you still have only 4 units (or ones)? No, you have 14, so let's write a small 1 next to the four so we can remember that you changed a ten for ten ones.
I have heard of some people diong the left to right thing, but luckily my school still does right to left and the "borrowing" but now it is called regrouping.
If you are teaching him right to left, here is a cute rhyme that will help him remember whether or not he has to "borrow"
Look at the numbers in the collumn and say "more on the top, no need to stop (just subtract). More on the floor, go next door and get ten more (borrow). Number's the same, zero's the game(answer is zero). Hope that's easy to understand over the computer!
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