We love doing “Math Before Bed” as part of our “read at bedtime” routine. We get out of the habit sometimes though because we also love to play card games (UNO, Go Fish, Old Maid, Memory) before bed. Last night I pulled up this picture:

I quickly counted them: 10 per column, 4 in each row. 40.

My 8 year old started counting by ones. She said, “I think there are 38.” Knowing she was not correct, I asked, “Besides counting by ones, how else could you find the answer?” At the same time, I started counting the far right column. Only 9. Hmmm. I counted again. Yup. I had assumed all 4 columns had 10. We chatted about this. We talked about how we could use my original answer of 40 to find the answer. “There are 2 missing from the last row! How can we use that?” She had a bit of trouble figuring this out. She kept saying, “10, 20, 30, 40.” over and over. I said, “Well, 40 but two are missing. Maybe someone ate them!” She counted backward to 38 and we were done.

Then she asked, “Can I make my own picture like this tomorrow?” So that is what we have just finished. She decided to use plasticine. I was recruited to mix colours together and help her make tiny balls. She decided she needed 60 of them. She also decided she wanted to do rows of three because 2’s and 5’s are too easy and she likes a challenge. (HOORAY!!!) After counting over and over by 3’s, making a few mistakes along the way, I prompted her to notice that there were 10 in a column. “10, 20, 30. Oh. Halfway there.” 🙂

In the end, we had more than we needed. She put those into groups of 5 (and one group of 4) to figure out how many were left. “5, 10, 14,” she said. It’s so interesting to me that she can skip count, but often counts by ones. She says this is because “ones is more easier.” She only switches to larger numbers and skip counting when she has a lot of things to count. I suppose this makes sense.

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## Published by Lisa Corbett

I live in Ontario, Canada. I teach. I hang out with my children.
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What an interesting discussion. I’m also fascinated that she wanted to make her own – more evidence that math really does develop through exploration rather than simply memorizing algorithms. My boys are with their grandparents right now, but I may show them the marshmallow picture when I see them next. I made the same error you did – I wonder what they will do?