Guided Lessons
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# Sharing the Subtraction Process

In this lesson, students will practice explaining the process of subtracting numbers up to 1,000 using base-ten blocks and peer feedback. Use this lesson on its own or as support to the lesson Fluently Subtracting within 1,000.
This lesson can be used as a pre-lesson for the Fluently Subtracting within 1000 lesson plan.
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This lesson can be used as a pre-lesson for the Fluently Subtracting within 1000 lesson plan.
##### Academic

Students will be able to solve subtraction problems within 1,000.

##### Language

Students will be able to explain subtraction with regrouping using base-ten blocks and peer interaction as support.

(3 minutes)
• Ask students and turn to a partner and discuss the term subtract. Ask them to think of how they would explain the concept of subtraction to someone that does not know the meaning. Ask them to think of keywords or phrases that relate to subtraction (e.g., "take away," "difference," "how many are left").
• Have students share their responses with a whole group and document their background knowledge on a piece of chart paper. Leave the chart paper on display for the rest of the lesson.
(10 minutes)
• Go over the tiered vocabulary words for this lesson by showing each vocabulary card on the document camera. Have students repeat the word and its definition. Then, invite student volunteers to describe the associated image and how it relates to the word.
• Introduce base-ten blocks to students. Hold up each block (hundreds, tens, and ones) and make sure students are familiar with each type and its value.
• Draw a place value table up to thousands on a piece of chart paper. Draw the symbol that represents each base-ten block in each column it pertains to (an empty square for the hundreds block, a rod or vertical stick for the tens block, and a dot for the ones block).
• On the chart paper with place value table, show the subtraction problem 365 - 183. Write out the following steps on a separate chart paper:
1. Write both numbers in expanded notation in the table (i.e., 300 in the hundreds column, 60 in the tens column, and 5 in the ones column).
2. Make a model with the base-ten blocks (3 hundreds, 6 tens, 5 ones).
3. Subtract the ones (regroup if the first digit is less than the digit you subtract).
4. Subtract the tens (regroup as needed using base-ten blocks to help).
5. Subtract the hundreds.
6. Check your answer by adding the difference to the number you subtract.
• Model how to solve the subtraction problem 365 - 183 according to the steps above on the chart paper. Draw models of base-ten blocks and cross them off as you subtract.
(10 minutes)
• Tell students that they will practice subtracting two to three digit numbers using the place value chart and expanded notation. Inform them that they will practice explaining the steps they use to solve the problem.
• Hand out scratch paper, base-ten blocks, and the Subtraction with Regrouping: Focus on the Fundamentals worksheet to students.
• Read the directions and the sample problems at the top of the worksheet. Point out the saying written at the top, "More on the floor, go next door and get 10 more!" and have students turn to each other and say what they think this phrase might mean. Explain to them that it means that if the number you are subtracting is greater than the number on top, you should regroup the higher place value and add it to make a number that you can use to subtract.
• Place them into effective partnerships. Tell students to work on the first problem (452 - 237) on their own. Inform students to do their best to write their process of solving this problem in complete sentences on the piece of scratch paper. Remind students to add drawings and models of base-ten blocks to explain their process further. Then, have them share their written explanation to their partner. The partner is to provide feedback on their explanation with the following questions/sentence stems as a guide:
• "What do you mean when you say...?"
• "Could you clarify how you did this part?"
• "What step did you take to solve this step?"
• "This sentence might be better if you said..."
• Tell students that these are sample feedback questions and that they may use other sentences or questions to give their partner feedback.
• Give students time to revise their written explanation of the steps to subtract on their scratch paper. Encoruage students to rewrite their explanation by adding words, numbers, and phrases based on their partner's questions and suggestions.
• Have the student reshare their explanation with the same partner. Tell students to compliment their partner for providing a clearer explanation of their work. Provide the sentence frame: "I like how you ____ in your revised explanation."
(8 minutes)
• Scramble the partnerships so students get the opportunity to work with another classmate.
• Instruct students to choose any of the problems from the worksheet (#2–#9) for them to solve using the base-ten blocks and the written steps to help them write out the explanation of their solution again.
• Have students repeat the process of solving, writing the process, sharing, getting feedback, revising, and resharing for two or more problems, time permitting.
• Revisit the chart paper you created with students on the word "subtract" during the Introduction. Invite students to add on to or change the chart by modifying their original ideas or adding symbols, pictures, or number sentences to the word web.

Beginning

• Have students repeat and rephrase the directions in the lesson.
• Display a word/phrase bank with pertinent language to be used in the lesson. Use images and examples in the bank to help solidify understanding.
• Provide bilingual resources such as online dictionaries or glossaries to help students look up unknown vocabulary words in their home language (L1) or in English (L2).
• Pair students with advanced ELs who are able to assist them in the partner activities.
• Pull aside a small group of struggling students and preteach a lesson just on place value meaning.

Advanced

• Ask students to rephrase instructions and important learning points throughout the lesson.
• Encourage students to converse with their partners without using the sentence stems/frames for support.
• Have them be first to share their math process during group sharing time.
(5 minutes)
• Distribute a blank copy of the Frayer Model and display a teacher copy on the document camera.
• Model how to complete the worksheet with another math word, such as "addition."
• Tell students that they will complete the model with the term "subtraction with regrouping."
• Collect the completed models to use as a formative assessment to check for students' understanding of the work they did in this lesson.
(4 minutes)
• Ask students to reflect on the lesson they completed. Ask the following questions as a guide:
• Was it helpful to have the opportunity to share your subtraction solution, get feedback, and then reshare? ("It was helpful/not helpful to have the share, get feedback, and then share again because...")
• When might we use this sharing strategy again? ("We might use this strategy again to practice...")
• Invite students to think and talk with a partner before sharing their ideas with the whole group.

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