DECIMALS ARE BRUTAL!

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Home : 2003 : October : 10

DECIMALS ARE BRUTAL!
By HEIDI

I feel your pain. I just started decimals in my grade 4 /5 class and it was rough going for awhile. They found the hundreds grid a difficult concept at first becuase they have always known the flat to represent 100, not
one. Try starting with a place value chart, but leaving the columns to the extreme right blank for now. Talk about the tens place, the ones place, the hundreds, etc. Then do a Sesame STreet style activity with the class. DIvide them into two groups. One group says the "th" sound. Then the other group says the "s" sound, then get them to take turns faster and faster until they says

"ths". This leads into talk about the fact that not all numbers can fit on a regular place value chart like the one they see. What if a person is 10 and a half, for example? Where would you put the half? That's why we have a decimal. Decimals like to hang out at the end of any regular number. SOmetimes you don't even see them, but they're there. Just hanging out. 75 is really 75 decimal. And if you want to say you have more than that, but just a bit more, you need to add a new column to the place value chart. Tenths. Then add hundredths and thousandths.

I find once they have the place value chart, if I show them a flat and place it in the ones column, they can see that the next smaller breakdown is a rod which would have to sit in the tenths, then a unit sits in the hundredths place. If they see the lineup right on a place value chart, they are much more capable of talking about how the flat can break up into 100 pieces, or hundredths. We did this for a long time bfor I changed the rules again to introduce thousandths. To do that I showed them the big cube sitting in the ones place, they knew right away that the flat had to come next and the tenths place was where it went, etc. I made a big deal about how we "changed the rules" about flats. And "changed the rules" again when we decided a big cube would represent one. They have gotten quite good at drawing the base ten representation of decimal numbers. And regrouping has come naturally.