## Saturday, December 31, 2016

### Subtraction without Borrowing Freebie!

As a first grade teacher, it's my job to help my students gain an understanding of mathematical procedures-- not just show them how to do something and drill it.

Even understanding that the number 26 is made up of 2 bundles of 10 and 6 individual "ones" is a tricky concept!  So, when it came time to teach subtraction of double digit numbers, I wanted to help my kiddos visually understand what they were doing.

### Getting Started

To start teaching this tricky concept, I gathered my first graders on our classroom carpet for our "mini lesson".  We talked about how we already knew how to do subtraction within 12 and I got them excited by telling them that by the end of the week ALL of them would be able to subtract numbers within 99!

I wrote the problem 43 - 21 = ____ on the board and told my students we could do this together!  I "stacked" the numbers on top of each other (something we had done before) and then I asked for a volunteer to tell me what 43 really stood for.

Hands shot up and together we grabbed some place value blocks to represent the number 43.  We put four ten sticks and three ones cubes under our document camera for all to see and I explained that if we wanted to do the problem 43 minus 21 we could just take away one "ones cube" and two "tens sticks" since that is what 21 really means.

We did this a few times with different numbers and then I showed them the visual worksheets I had printed double sided.  Some of my first graders grabbed place value blocks to use, and some students just crossed out the pictures on the paper!

I checked in with each student to make sure they were starting in the ones place-- to prepare them for when they eventually will have to "borrow".  I also made sure each student understood that they could always visit our math manipulatives bookshelf for materials!

The next day, we revisited subtracting double digits and I had my kiddos do the next practice sheet.  I let my early finishers color the clipart on the page, and we made sure to re-gather on the carpet to discuss our learning thus far!