It's that time of year! No, I'm not talking about leprechauns and rainbows... and it's not spring yet (in this neck of the woods I don't think that's happening for quite a while!)... Nope, it's time for some addition and subtraction with regrouping in second grade. Help. Me. Now. The addition part usually goes ok, especially since we've begun teaching it in January instead of earlier in the year. Most of my kiddos get a handle on that pretty quickly. No... it's the SUBTRACTION with regrouping that makes their little heads spin.
Thankfully, I have a great tool that I use to help my kiddos really grasp the concept of subtraction with regrouping. It's a type of base-10 board called a "Transition Board" - and it works beautifully! (You can click HERE to see my post on using the boards for addition with regrouping and on how to make them.)
Thankfully, I have a great tool that I use to help my kiddos really grasp the concept of subtraction with regrouping. It's a type of base-10 board called a "Transition Board" - and it works beautifully! (You can click HERE to see my post on using the boards for addition with regrouping and on how to make them.)
Here's how it works for subtraction with regrouping. Start with the board held so the sticker is at the BOTTOM.
We'll work through the steps to solve the problem 82-47 = ?
Show the top number with base ten blocks in the first row of the board.
Then use number cards to show the second number in the problem underneath. (I printed out squares with numbers 0-9 and had my kiddos cut them out. Nothing special, although I did have a laminated set I used for a few years.)
Now start with the ones. Here we have 2 - 7. Do we have enough ones to do that? (I always have my students talk through how they know if they have to regroup or not. Many of them will regroup for EVERY subtraction problem they see now, and it's important for them to stop and think about what they need to do.) The number cards are in the red area because that is the "decision" area - we have to decide if we're going to regroup or not.
Since we do not have enough ones, we need to regroup. Take a tens rod from the tens column and move it to the ones column. (I have them move the ones that are already there up a little so they don't get them confused with the regrouping that's abut to happen!)
Now take ten NEW ones and line them up above the tens rod. (This can be tricky - make sure no one is using the ones already on the board.)
Slide the tens rod off the board. How many ones do we have now? Do we have enough to subtract now? (I will also ask my students to tell me how much I have on the board now,, so they can see that even though we traded, we still have the same numbers we started with, just looking different.)
Since we now have enough ones to subtract, put 7 ones on the number card.
Slide the ones (and the card underneath) off the board.
Move the remaining ones down to the bottom of the board in the answer area.
Go back to the top and look at the tens. Can we subtract? In this case, yes. Place 4 tens on the number card.
Slide the tens off the board.
Move the remaining tens down to the answer area.
Ta-dah! We have our answer!
Honestly, the first we do it there's a lot of confusion and jumping ahead and mixing things up. That's ok. I try to have students work in small groups and we go ONE step at a time. By the time we get to the third or fourth problem, many of them have caught on and know exactly what to do.
After most kiddos can easily solve problems using the board, we move on to seeing how the algorithm matches what we did on the board, then finally to using just the algorithm. But that's another post!
If you have any questions about how to use the boards for subtraction, just ask! Some kiddos only need the boards for a few problems - others continue to need the support for a bit longer. Either way, I find that by having students using the transition boards, they have a better understanding of the regrouping process and are not just going through the motion with the algorithm.We'll work through the steps to solve the problem 82-47 = ?
Show the top number with base ten blocks in the first row of the board.
Then use number cards to show the second number in the problem underneath. (I printed out squares with numbers 0-9 and had my kiddos cut them out. Nothing special, although I did have a laminated set I used for a few years.)
Now start with the ones. Here we have 2 - 7. Do we have enough ones to do that? (I always have my students talk through how they know if they have to regroup or not. Many of them will regroup for EVERY subtraction problem they see now, and it's important for them to stop and think about what they need to do.) The number cards are in the red area because that is the "decision" area - we have to decide if we're going to regroup or not.
Since we do not have enough ones, we need to regroup. Take a tens rod from the tens column and move it to the ones column. (I have them move the ones that are already there up a little so they don't get them confused with the regrouping that's abut to happen!)
Now take ten NEW ones and line them up above the tens rod. (This can be tricky - make sure no one is using the ones already on the board.)
Slide the tens rod off the board. How many ones do we have now? Do we have enough to subtract now? (I will also ask my students to tell me how much I have on the board now,, so they can see that even though we traded, we still have the same numbers we started with, just looking different.)
Since we now have enough ones to subtract, put 7 ones on the number card.
Slide the ones (and the card underneath) off the board.
Move the remaining ones down to the bottom of the board in the answer area.
Go back to the top and look at the tens. Can we subtract? In this case, yes. Place 4 tens on the number card.
Slide the tens off the board.
Move the remaining tens down to the answer area.
Ta-dah! We have our answer!
Honestly, the first we do it there's a lot of confusion and jumping ahead and mixing things up. That's ok. I try to have students work in small groups and we go ONE step at a time. By the time we get to the third or fourth problem, many of them have caught on and know exactly what to do.
After most kiddos can easily solve problems using the board, we move on to seeing how the algorithm matches what we did on the board, then finally to using just the algorithm. But that's another post!
Give these a try, either with your whole class or just a small group and see how they go. We teachers ALWAYS need more tools in our toolbox!
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