More Subtraction Action

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SWBAT subtract one number from another. SWBAT use numbers and expressions to record.

Big Idea

We can't forget about addition's inverse little brother, SUBTRACTION! Students will engage in subtraction fact fluency game.

Warm Up

5 minutes

I start this part of the lesson by asking the kids to sit in front of the classroom number line.  

"Today we are going to change up our Start At/Stop At routine.  We are going to use the numbers between 90 & 120."  I am going to ask you to give me a number between  90 & 120.  Who can give me a number between 90 & 120?  Who could give me another number between 90 & 120?. I will put a green dot on the first number given and a red dot on the 2nd number."  

You should put a green dot on one stick it note and a red dot on the other.  These will be used to focus on where to start and stop.  You can also practice counting back by placing the green dot on the larger of the two numbers given.  I will call ons students to come up and point as the class counts.

I will ask a student to point to each number as we count as a whole group.  I will continue this process as time allows.   In this case students are counting up to and back from 120, starting at any number (CCSS.Math.Content.1.NBT.A.1).  This routine is the process in which I can assure that the students are continuously working toward this standard. I have been moving to higher numbers as the year progressed.  Now that we are in the final trimester, I want to focus the 90-120 range.  THis will assure that I have covered the CCSS expectation for 1st graders.

Introduction to Subtraction Game

15 minutes

Advanced Preparation:  You will need to make enough copies of the recording sheet (from the section resource) for your students to be able to play several rounds of the game.  You will also need a 1-6 dot die and a 7-12 number cube for each team.  You will also need to have a recording sheet on an easel for everyone to see.  

"We have been spending a lot of time making sure that our addition facts are fluent.  I want to make sure that you are as equally fluent with your subtraction facts.  You are going to play a game today that allows you to practice your subtraction facts and helps you build fact fluency with them.

I want you to watch how the game works.  You will first roll the two die.  One die has the numbers 1-6 with dots for each number and the other die has the numbers 7-12 with numerals.  Your job is to roll both die at the same time.  You must then subtract the number on the dot die from the number on the other die.  Then you should record your expression on the recording sheet in the column of the difference."

The ability to record their expression is an example of students modeling with mathematics (CCSS.MATH.PRACTICE.MP4).  It is important to know that they are recording expressions and not equations at this point.  The lack of an = sign prohibits these to be labeled as equations.

"Let's play few rounds together."

I then will model with cubes, with a number line, and finish with counting back from the higher number.  I all ask students to assist me in this modeling.  In this case, students are using tools to assist them in their computation and are building concrete models (CCSS.MATH.PRACTICE.MP5).

"Remember, you can use any of the approaches that we talked about or you can also just state the fact if you know it.  When I come to your group, I will want to see which strategy you are using."

The CCSS expects 1st grade students to relate counting to addition and subtraction (CCSS.MATH.CONTENT.1.OA.C.5).  In this case the students are using approaches that allow them to start at a number and count back, which helps support their engagement with this CCSS expectation.

Station Time

30 minutes

The students will now play the game that I just introduced.  They will play in partners and can choose their own team.

As students are working, I will circulate and observe which facts students fluently know and which ones students need to use cubes or a number grid for.

Differentiation:  I have two students who I know are fluent with their subtraction facts.  I am going to teach them a different game that focuses on subtracting numbers (6-9) from the numbers (11-15).  There is a recording sheet for this game that is also located in the section resource for students working at this level. 

Both of these games have students subtracting within 20 and building fluency within 10 (CCSS.MATH.CONTENT.1.OA.C.6).  This is a CCSS expectation for first grade students.  

Explaining Their Thinking

15 minutes

I will gather the students back to the carpet for this part of the lesson.  I will lead a discussion on strategies that the students used to solve the problems ask a few students how they solved the problem.

This is where it is important to know which strategies students are using to solve their subtraction facts ahead of time from observing while they were in their stations.  This way you can be intentional with who you call for sharing.  I want to make sure that any strategy that was being used is represented in the discussion.  I want to end with the strategy of modeling the counting back using the dot cube strategy.  This way the students finish the discussion hearing this important and efficient strategy last.  

"I am going to tell you a fact that I saw rolled today.  I want you to solve this quietly, and then put your thumb on your chin when you have the answer.  I will then call on some of you to share your strategy.

  • One student rolled a 11 and a 5.  What number did he fill in on his game board?
  • Another student rolled a 11 and a 4.  What number did she fill in on her game board? 
  • Did anyone use the first problem to help them solve the second problem?  How?"

 The students are solving word problems within 20, involving subtraction situations.  The CCSS expect that 1st grade students can represent and solve these types of situations (CCSS.MATH.CONTENT.1.OA.A.1). During this discussion, the students are expressing how they solved the problem and/or elaborating not he strategy that they used.  Their peers are comparing to their own strategy and critiquing the approach of others (CCSS.MATH.PRACTICE.MP6)

Continued Practice

5 minutes

I will ask the students to meet me on the carpet and hand out their sheet for today's Mad Minute exercise.  This routine was introduced in a previous lesson.  Please check out the link to get a full overview of this routine.

I want to really focus on fact fluency and build upon the students ability to solve within ten fluently (CCSS.MATH.CONTENT.1.OA.C.6).  I am going to use the Mad Minute Routine.  This is a very "old school" routine.  However, I truly feel students need practice in performing task for fluency in a timed fashion.  Students need to obtain fact fluency in order to have success with multiplicative reasoning.  Students who don't gain this addition fact fluency by the end of 2nd grade tend to struggle with the multiplicative reasoning in third.  Having this fluency also allows them to work on more complex tasks because the have the fact recall to focus on the higher level concepts.