# Roll a Subtraction Problem

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## Objective

SWBAT properly structure and solve subtraction problems by rolling a dice and writing the numbers in the proper order and solving.

#### Big Idea

Kindergartners struggle to understand the structure of subtraction problems. The idea that the larger number must come first is difficult for them to understand. This lesson requires them to use that understanding in order to play the game.

## Daily Calendar & Counting Review

15 minutes

Each day we begin our math block with an interactive online calendar followed by counting songs and videos.

Calendar Time:

We do calendar on Starfall every afternoon.  This website has free reading and math resources for primary teachers. It also has a  “more” option that requires paying a yearly fee. The calendar use is free. A detailed description of Daily Calendar math is included in the resources.

Counting with online sources: Today we did counting practice to reinforce the counting skills. We watched two to three number recognition 0-10 videos (one to two minutes each) because some of my students students were still struggling with identifying numbers correctly in random order. We watched"Shawn the Train" and counted objects with him to refresh our memories on how to count objects to ten and to reinforce one to one counting. Since we have started the second quarter of the school year, we added to today's counting practice: counting to 20 forward and backcounting by tens to 100 and counting to 100by ones to get a jump on our end of the year goals.

## Direct Instruction

10 minutes

This lesson is an extension of the previous lesson, 10 - Minus Roll a Number. In this lesson the focus is on the structure of a subtraction problem with the emphasis being on the fact that the largest (the minuend or whole number) comes first and the smaller numbers (the subtrahend and the difference) follow the minuend (I use whole number with my kinders).

We sing and view the video, When You Subtract with a Pirate by Harry Kindergarten. This gets the kids motivated and thinking about subtraction.

We review what we learned in the previous lesson. I place the game board from the previous lesson under the doc cam and play a couple of rounds. As I play, I emphasize that the 10 always is written first in the problems and that whenever we create a subtraction problem, the largest number always comes first because we take away from the largest number (the whole number) to get the two parts (the subtrahend and the difference).

Next I place the new game board under the doc cam and I tell the kids that I am going to demonstrate what they will be doing today.

I roll the dice and it is 4. I tell the kids that I need to remember what I rolled. I have a student come up and roll the dice. She rolled a 2.

I say, I rolled a 4 and Anelyse rolled a 2. Which number is bigger, 4 or 2? All the kids yell out 4. I say, "Okay, then I must write the 4 first in this equation" and I write 4 on the first line of the problem.

I then write the 2 on the next line and read and solve the problem while thinking aloud. "4 minus 2 equals...I draw four dots and cross out 2...the answer is 2."

I do this for several rounds until I hear the kids joining in and telling me what to do step by step. That tells me that they are almost ready to take it on for themselves.

## Guided Instruction

10 minutes

For guided practice, I have the kids sit at their tables with their math partners.

I direct the play of the game for the first several rounds step by step. On occasion, I have had to direct game play for the entire lesson because some groups understand it sooner than others. My class this year is a little slower at grasping skills and procedures than classes I've had in the past because over 50% of this year's class was only four when the year started and they did not begin turning five until October.

Steps to the game (played with recording sheet in plastic sleeve & dry erase marker):

Partner A (always the stronger math student) rolls first and states his/her rolled number.

Partner B rolls and states his/her rolled number.

The partners decide which number is larger and the partner with the higher number writes that number on the first line (in the number sentence).

The partner with the smaller number writes that number on the second line.

Together they solve the problem. They draw the larger number of dots and cross out the smaller number. They count how many are left and write that number on the answer line.

The next round begins with Partner B rolling first.

We continue like this until I see the kids confidently and naturally moving a step ahead of me in game play. That's when I know they have they have a firm understanding of the steps and the process.

## Independent Practice

15 minutes

Once we have made it to independent work time (game play), which may take a day or two to reach depending on your class, i let the kids take off with the game and I roam the room to intervene as needed for behavior and assist with confusion and/or inaccuracies.

The goal of the independent time is for the kids to understand that the larger number must be the number that is subtracted from. It is imperative that they learn the structure of a subtraction problem. Conceptual understanding of mathematics is most important for kids to be able to build up to higher level mathematical thinking.

I bring kids to the floor for intervention and support if I see them struggling to understand how to set up or solve s subtraction problem. I provide additional guided practice with think alouds to assist in solidifying the steps and the structure of subtraction. Many times it's just a matter of hearing and seeing it over and over again before fully understanding it. Exposure and experience usually resolves the struggle over time. Asking higher level questions like, "Why do you have to take the smaller number away from the bigger number?" helps tremendously. Children who have to share their thinking understand what they are doing much more clearly.

## Closure

10 minutes

I gather the kids back together on the floor and we share our experiences that we had playing the game.

I ask the kids to share any challenges that they may have experienced.

We discuss anything that they found confusing and we celebrate everything that they learned.

Students are also welcome to share any ideas that they may have to improve the activity or build on it to make it a more meaningful experience. This creates buy-in for the kids. The realize that their opinions and ideas are important to me and I validate them by making adjustments to the activities.

## Exit Ticket

5 minutes

The exit ticket is a short page with 6 random subtraction problems. At this point, I look for accuracy in the solution not the structure of the problem as this is the first time they are asked to play this game and consider the structure as important.

If this game is played repeatedly throughout a week, I would expect the kids to be able to set up a problem when given two random numbers between 0 and 10 and solve it.