We throw the
term around but rarely define it. I had
two experiences this week that help bring the concept into sharper focus.
I was
fortunate enough to work with second graders on Oahu, in a Hawai’ian language
school. I had beansticks and bundles
and leftovers with me. After the keiki
(children) became familiar with beansticks, I posed this question to them; “Build
the number that is 1 beanstick and 15 beans.”
All children
were able to figure out it equaled 25. But some children built it with two beansticks
and 5 loose beans and some did exactly what I’d asked. Then we had to discuss if both answers were
correct and equal. It led to a lively
discussion and some very strong opinions!
It was
developmentally interesting to see the children struggle when we moved to
bundles and leftovers. Since they couldn’t
see the 10s as clearly, building one bundle with 20 ones was much more
problematic. The children spent a great
deal of time taking the bundles apart, counting 10s, and putting them back
together. Obviously, they didn't trust my
bundling skills!!
My second
experience was sitting in a workshop with Dr. Yeap Ban Har, our favorite expert
from Singapore. He talked about number
sense as a complete understanding of number bonds. Our children need to understand 25 is 20 + 5,
but also 10 + 15. Without this
understanding, they won’t be prepared for regrouping. As they get older, that understanding needs
to generalize. 3/5 is 2/5 + 1/5. If one dividing 351 by 3, it doesn’t help
much to break the number into 300 + 50 + 1.
Number sense means the child understands that 300 + 30 + 21 is a much
more logical way to decompose the number.
Ban Har will be joining us at our National Conference for Singapore Math
on July 9-10.
Try posing
some number sense questions to your students and then give them some time to
struggle with the concepts. Don’t jump
in and help too soon!
