# Subtraction in Context II

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## Objective

Students will be able to use the standard subtraction algorithm, and apply the algorithm to solve word problems while utilizing Math Practice Standard 3.

#### Big Idea

Students solve one step subtraction word problems while practicing skills to master Math Practice 3.

## Warm Up

5 minutes

Students will begin this lesson with rounding numbers to the nearest thousand, ten thousand, and hundred thousand using a strategy I call Pass and Read.  Each student has an index card.  I have them think of a four digit number, a five digit number, and a six digit number.  They record these numbers on their index card.  They then round each of those numbers to the largest place.  Students should do this quickly. I only give them 3 minutes.  If they don't have an answer at the end of three minutes, this is sign to me that they need more practice with rounding or building number sense.  The directions for pass and read directions are located here.

I chose to do a rounding review for today's warm up since students have a place value assessment coming up.  I am able to observe students who need more support with this concept and reach them before the assessment.

## Concept development

45 minutes

I start this lesson by introducing the "new phrase that pays,"  To solve this problem I ______. Today's lesson will focus on Math Practice Standard 3 by having students communicate their math thinking.  As stated on www.insidemathematics.org, teachers who are developing students’ capacity to "construct viable arguments and critique the reasoning of others" require their students to engage in active mathematical discourse. This might involve having students explain and discuss their thinking processes aloud, or signaling agreement/disagreement with a hand signal.  I let students know that I want to catch as many students as I can using this phrase.

Students have had several opportunities to solve word problems with their learning partner, today they will work independently for 5 minutes and then turn and talk for 2 minutes.  The 5 minutes of independent working time is usually enough time for students to solve one word problem, draw a tape diagram, and check their work. Students will solve the word problem, follow all directions, and when I give a signal,  they talk to their learning partner. I use the website www.timeme.com so students can also visually observe the time left.

During the two minute talking time, I listen for students who are using the phrase that pays as well as listen for students who may disagree on answers.  (The linked short video clip shows two students revising their work during the 2 minute talk time.  You can hear the boy saying, "So, I think you're right.")  This is a very quick two minutes and my classroom buzzes during this activity.  I chose specifically one step subtraction problems with large numbers for this activity because I wanted to concentrate on the phrase that pays.  If I had done two step word problems, students would need more time and energy to focus in on the content of those problem. By using the one step word problem, my students are still able to work towards mastery of 4.NBT.4 as well as master strategies and models to be used in order to master 4.OA.3 which states students will solve multistep word problems. When my students are confident in their math thinking, and using models to make sense of mathematical situations, I believe they will be more ready to tackle 4.OA.3, but I will begin with smaller numbers in my  next unit.

When the two minutes are up, students resume working independently.  Students may chose to revise any work if their partner has convinced them of a different answer or strategy.

Students are able to complete the word problems in the time allotted.  They work on the front side as homework.

Students using phrase that pays shows students talking during the 2 minute talk time.

## Student debrief - Wrap up

5 minutes

To wrap up this lesson, I ask students why it is important to communicate their math thinking.  I then ask them what mathematical practice they used today and direct their attention to the posters in my classroom.  Many students respond with phrases like: "We can learn from each other," "_______ might have another way of doing the same type of problem that makes more sense to me," and "When we talk about our thinking it helps our brains grow."

This last phrase is specific to my students. I talk a lot about the brain and how it grows and myelinizes. Myelin is white matter in the brain that forms layers that make nerve impulses faster and stronger and which a number of researchers suggest increases learning. The amount of myelin and its density seems to increase through practice and makes what you are learning to do more automatic. The idea of deliberate practice comes in because we have to ensure that myelin forms to increase and strengthen the right impulse.  For more information about student learning and myelin, you can check out this blog post. The author, Larry Ferlazzo, discusses current events, trends, and educational issues and interests. This is a blog I follow and check weekly.