793 X 10 = 7,930
793 x 100 = 79,300
793 x 1000 = 793,000
- What do you notice about the above expressions?
- What is happening to each of the digits of 793?
- Write the zero rule for multiplication as you understand it?
- Explain why the zero rule for multiplication works using your understanding of our base ten place value system.
These questions served as the heart of a math workshop last month when I visited lab hosts Andrea Overton and Rachel Gardener’s fourth-grade classroom at STEM Launch school in Thornton, CO. They dispensed with the typical worksheet featuring rows and rows of multiplication problems and instead sought to highlight conceptual understanding by inviting learners to look deeply at just a few expressions.
Students dove independently into their “thinking sheets,” responding in writing to the questions above. Then their teacher brought a small group together for conversation. A student listening to a peer exclaimed, “Oooh!” and Rachel turned to him with an invitation to share his brain’s growth.
“My brain growth is that when you add a zero, it’s growing by ten. When you add a zero, you are basically making your number bigger by ten.”
Another student chimed in, “That makes a lot of sense to me now. I didn’t get it at first, but now it made a lot of sense.”
Rachel affirmed, “You didn’t give up when it didn’t make sense. That shows me you have a lot of perseverance.
Another student inquires, “So, you just add the zeroes?”
Rachel asks, “I heard you say, ‘just add those zeros.’ Why would you do that?”
A third student explained, “ It is because of the place value chart when I am making a jump…” as she began to explain, Rachel realized an illustration would help the group understand and invited this learner to the board. She drew:
She showed how each column goes up by ten and explained, “To get to ten from one, you have to make one jump…”
Rachel revoiced, “What I heard you say is if you move that seven over one jump, and everything moves over one jump, you are multiplying by ten.” Then she pointed to the one’s place and asked, “So, what comes over here?”
“Zero!” several students replied.
“What is the zero representing?”
“We are starting to understand.” Rachel affirmed these learners, then asked them to self-assess using thumb signals, their own sense of the zeros rule. “Show me where you are.”
To learn more about teaching math for understanding and to see a lab classroom like Rachel and Andrea’s in action, join us for the PEBC Minds on Math Institute Dec. 12 – 13, and sign up for the Dec. 14 lab.