Subtraction Number Talks

This week we worked through Chapter 4 in our on-line book study of Making Number Talks Matter.  This chapter deals with various subtraction strategies.  I was a bit nervous to actually jump in to this for real, but it has been really fun and my sophomores (2 classes worth) seem to really enjoy it.

My classes did two subtraction number talks this week.  I invited my principal to come see me do the second one.  I thought I would be nervous, but my classes really get in to these (I had done several dot talks with them) that I was pretty sure THEY would be fine.  I am such a novice at this, I wanted her to come observe me to see if I was making sure not to call on too many boys, not trying to correct "weird thinking", etc.  I sent her a picture of my second planning guide.  Here are both the planning guides:

Here are some board shots for the first number talk.  I neglected to get shots of the second talk!

The one over on the right really through me for a loop.  I asked her to help me understand how she was doing this, and this was the best she could do.  I thanked her for sharing and then took a few more volunteers.  

When we were all done I pointed out to the young woman that it looked to me like the person who shared below her share, did pretty much the same thing, except they noted that the 5 and 2 really means 50 and 20.  Now I am asking readers: how would you deal with the 8-3 thing?  Do you just point out at the end that you can just subtract in the order you see?  That would 60 - 20 to get 40 and 3 - 8 to get -5....combine these and you get 35.

We were done, wrapping things up and one young man asked if he could PLEASE share his strategy?  How can you refuse?  And it was gorgeous.

"I took 20 from 60 to get 40, then took away the 8 to finish the 28 and got 32, but I still was 3 short from the 60, so I added it back in to get 35."






The principal was really impressed by the number of strategies and the "OHHHS!" when someone shared a new strategy.  She is hoping that after I have had some more practice, I will feel comfortable being video taped.  I am also open to have people come in a visit to see how this is happening.  It is pretty amazing!

I am SO grateful for this book study. It is forcing me to do the talks, which could easily have gone by the wayside since there is SO much else I need to get done.  These have been worth it, though!!