Teaching 10 more and 10 less is a big standard to start working on in the first grade. The hardest part of the standard is that it requires students to it mentally. That’s right! It says mentally in the standard and it is the key word!
Given a two-digit number, mentally find 10 more or 10 less than the number, without having to count; explain the reasoning used.
I created a unit that starts with a lot of support from the hundreds chart. We have to take baby steps before we can walk. I knew that I could not expect my students to know how to mentally add and subtract with the number 10 from any number. From there, I scaffold the support from the hundreds chart and slowly take it away.
I love teaching math and when I came up with this idea, I was beyond excited. I knew that I had found a really good way of showing the kids how to do 10 more, 10 less, 1 more and 1 less.
We started by using a full hundreds chart. It nearly takes up the whole page. At the top there is a small chart. The small chart is where students can write the answers to 10 more, 10 less, 1 more and 1 less. My class and I color coded this worksheet. We used yellow to color the number we were working with. Then we used blue to show 10 more and 1 more and we used red to show 10 less and 1 less. Some of my students stuck with this strategy throughout the entire unit. It really helped them visually remember.
Then I used a blank cross and made the hundreds chart much smaller. I wanted to start slowly taking away the hundreds chart so that students start to rely on mental math. The hundreds chart is still there, but really only for comfort. Some students had a difficult time with this, but when I reminded them that they could color code, a light switched on for them and they were ready to work. Using the crosses was a visual reminder to the hundreds chart to help them remember a bigger number and smaller number.
Next, I started to show parts of the hundreds chart. I would only give the students a small piece to work with. I also started having them turn the crosses into number sentences. I wanted them to make the connection between the visual representation and the mathematical equation.
Last, I gave them a task with a very small hundreds chart and 4 blank number sentence boxes. Although I didn’t completely take the hundreds chart away, I still made it very small. I also told my students to challenge themselves and fold their paper over so they couldn’t see it. Many of them were up for the that challenge.
My school district is lucky enough to have JiJi, so I know that the kids will get plenty of practice doing this standard mentally. JiJi has a great level that has students do 10 more and 10 less without a hundreds chart. When students get to that level, I remind them about hopping around the hundreds chart and they light up with a big smile.
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