To the left, to the left
Everything's ten times in the place to the left...
To multiply by ten on paper, however, we typically move the decimal point to the right. Ugh! That's confusing! My morning tutor buddies needed to move back to something more tangible, so we made some place value strips. It was easy and effective.
- Cut sentence strips into two-inch pieces.
- Give each student a whole sentence strip and ten two-inch pieces.
- Have each student make a decimal point in the center of the sentence strip then mark five place values (two-inch lines made with a ruler and a marker) on each side of the decimal point.
- On the two-inch pieces, have them write the numerals 0-9.
Here's an abbreviated version of what happened in our tutoring session:
Place eighty-nine hundredths on your strip. Students did this with no trouble. Yay!
Multiply by ten. Everyone knew that they were supposed to slide their digits, but some slid to the left and others slid to the right. Oh boy. We had to stop and talk about Beyonce, the fact that we should get a bigger number when multiplying by ten, and how each digit in the number should be ten times its original size.
Multiply by ten again. Good, everyone was on board.
Place three and nineteen hundredths on your strip. Success again.
Multiply by ten. Yes, I think we've got it!
Place seventeen and nine hundredths on your strip. Ugh-oh, watch out for place value! The nine should be in the hundredths place.
Multiply by one hundred. Yay! We're getting this.
Now place this number on your strip: fourteen thousand... Oh no! We have fallen apart. Fourteens are all over the place! It was time to go back to periods of three numbers (and put a comma on our strip to show where the thousands place ended). After several minutes of remediation, discussion, and practice, we were back on track.
Divide by ten. Yes! They slid their numbers to the right.
In my mind, a place value strip and moveable digits are completely necessary when teaching 4.NBT.A.1 (Recognize that in a multi-digit whole number, a digit in one place represents ten times what it represents in the place to the right.) and 5.NBT.A.1 (Recognize that in a multi-digit number, a digit in one place represents 10 times as much as it represents in the place to its right and 1/10 as much as it represents in the place to its left.) As an additional bonus, they really help students learn to build whole numbers and decimals, which is essential to writing them in standard form (4.NBT.A.2, 5.NBT.A.3).
This little teaching idea worked wonders in my classroom. I hope it's something that will help you too.