Here’s a portion of an email I received recently –
I still have several fifth graders who don’t get that 17-9, for example, is a basic fact….One of the students, on a WJ that I’m scoring, borrowed the 1 and made the 7 a 17, and didn’t know what to do and/or didn’t realize that it was the same problem she had started on.
I’ve seen student do this too. My suggestion is to pull out your 10-frames and and work on giving students visual models for +/- 10 and +/- 9.
- Use a full 10-frame with a partial frame to show teen numbers like 10+5 is fifteen, etc. Most students know this or catch on to this set of combinations quickly.
- Then use the frames to ask (and show), “What is 15-10, etc.?” Most will catch on to this quickly also.
- Then – leave both the full 10 frame and the partial frame on the table and ask “If 15-10 is 5, what is 15-9?” HOPEFULLY, they will see that they can subtract 10 and add one back on or move one of the dots from the full 10-frame over to the partial and take away the other 9. It might help to have to empty frames and use chips to fill in the numbers you want so students can actually move the chips around to show their thinking.
- You can also work on 9+addition using a frame with 9 dots and a frame with the other addend. (Again you might want to use chips so they can be moved around.) This really helps students see how you can make a 9+ problem into a 10+ problem. It’s a strategy that teachers talk about a lot but they just use bare numbers. The frames and chips help students see how it works.
So… to make a long story short, it all comes down to structuring and using visual models.