decimal woes - really long

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decimal woes - really long
By biz

I actually found your post online last week when I searched for decimal help myself. I came up with a printable paper for each student to really delve into tenths and hundredths (our standards). vanDeWalle suggests that students
need to understand that 6/10 + 8/100 = 68/100. I found it was really difficult for them to understand the step that 6/10 = 60/100 with only a hundreds chart.
...So, I put three grids on one half of a paper (all lined up vertically). The first one was a 100s grid (10 rows, 10 columns in Word - tables), the next was a 10s grid (10 columns, 1 row in Word - tables) and then a repeat

of the 100s grid below that. These were all equal sizes so they were easily comparable (you have to tweak the table size to do this).

The first instruction was to color 68/100 on the top 100's grid, label the fraction, and then name it in words orally (68 hundredths). Then they had to label 6/10 on the 10s grid, label the fraction, and name it in words (six tenths) and 8/100 on the last hundreds grid, label the fraction, and name it in words (8 hundredths).

When all three were correctly labeled we went back to the first and second grids (68/100 and 6/10). I covered up the 8/100 from the 68/100 and asked them to compare the 60/100 and the 6/10 - are they the same or different? You'll get both answers. I handled the different by asking them if I cut out the 6/10 and put it on top of the 60/100 if they would be the same size. "Yes....oh..."

So 6/10 + 8/100 = 68/100.

How do we write that as a decimal? Blank stares were the norm in my class.

I then drew up a place value chart for them ___.___ ___ and labeled the ones, tenths, and hundredths. I had them look back at the grids we had just labeled - how many tenths in 68/100s? 6/10. 6 goes in the tenths place. How many 100ths? 8/100. 8 goes in the hundredths place. They wrote out the decimal underneath the bottom grid. It would probably be useful for them to label each grid as a decimal as well (last step). I didn't do this but I think I will Monday if anyone is still confused but I think I caught them all.

We repeated this process with 3 or 4 more problems like that - building it, splitting it into 10ths and 100ths, and then naming it as a decimal.

I found that the most important step was being very conistant with language. Naming fractions as sixty-eight hundredths and then naming the decimal sixty-eight hundredths.

I would also suggest following up on this lesson with one where you have a whole number with a decimal as well so they understand what the decimal point means in relationship to larger numbers.

Hope this helps.