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After this lesson, students will have a better grasp on subtracting from 20.
- Invite the students to come together.
- Explain to students that today they will be exploring subtraction during math.
- Ask the students what subtraction means. Call on a few students to explain.
- Introduce the movement of bringing your hands in front of your chest in a clasp and bringing your hands behind your back in a clasp using a fluid movement as you say “Subtraction means taking away.” Invite the students to participate in this choral chant and movement.
- Create a chart titled "Subtraction" and record student ideas as they explain the meaning of subtraction. Include examples of situations that require subtraction with subtraction equations.
- Allow students to share their understanding of subtraction in their home language (L1) if possible.
- Prompt students to compare and contrast addition and subtraction.
- Define subtraction as finding the difference between two numbers. Remind students that with subtraction the whole and one part are known, and we solve for an unknown part. Provide a "whole-part-part" visual to illustrate this concept.
Explicit Instruction/Teacher modeling(5 minutes)
- Draw a number line up to 20 on the board.
- Write the subtraction problem 10-5= __ on the board.
- Model aloud how to solve the problem. Point out the subtraction sign and remind you students that subtraction means taking away. Use the number line to start at 10 and jump back 5 spaces.
- Review the number names from 0-20 in English. Provide a chart for reference.
- Gesture from left to right pointing at the number line and ask students what they notice about the numbers. For example, the numbers get bigger as you move to the right.
- Tell students to jump forward and repeat, "forward." Continue with backward, left and right.
- Ask students how they would use the number line to add, and how they would use it to subtract. For example, to add we would jump forward on the number line. To subtract, we must jump backward.
Guided Practice(25 minutes)
- Move the class either outside or to an indoor space large enough for all of your students to move around.
- Lay the number cards down in order in a line.
- Ask the students to gather in a circle around the numbers.
- Explain to the students that you will be pulling out a subtraction flashcard and calling on a student to solve the subtraction problem using the large number line.
- Model this activity for the students. Pull out a flashcard such as 6-3=____ and show the students how to find the number card 6 on the ground. Stand next to the number, then jump and count back three times until you land next to the number 3.
- Call on each student so that they have a chance to partake in the activity.
- Have students return to their seats.
- Review the meaning of the minus and equal sign symbols.
- Write the sentence frame "____ minus ____ equals ____" on the board. Instruct students to say a number sentence after jumping.
- Tell students to describe the steps to subtract using the number line in their own words to a partner. Emphasize that students will count the jumps between the numbers and not include the initial number in the count.
Independent working time(15 minutes)
- Pass out the Easy Subtraction Under the Sea worksheets, laminated number lines, and counting blocks, if necessary.
- Students may work in partners or groups for this activity and they should have the number line chart and access to blocks to solve the problems.
- Review writing subtraction equations horizontally and vertically. Model solving the first problem on the worksheet, showing students that the equal sign is written differently in vertical equations. Teach students to write the difference below the equal sign.
- Encourage students to check their answers using addition, and think about whether their answer makes sense.
- Prompt students to explain how they solved the subtraction problems.
- Ask students to explain how they know that their answers are correct. If students make errors, ask them to explain their thinking. Encourage self-correction of errors rather than rushing to provide a correct answer.
- Enrichment: Students who finish their math page early may play the whole body subtraction game inside the classroom with peers. They may come up with their own subtraction problems from 20 or use the flashcards.
- Support: The teacher can provide support for students who need extra assistance during the whole body subtraction game by helping them jump back the number of spaces necessary to solve their subtraction problem. During independent working time students who need extra assistance may be paired with a peer who understands the concept of subtraction well.
- Pay close attention during the whole body subtraction game to see which students understand the concept of subtraction.
- Rotate around during independent working time. This will help you to assess individuals, partners or groups who are struggling to solve the subtraction problems. Keep note of these students to impact your future instruction.
- Notice whether students are about to subtract accurately using the number line. Check that students are counting the number of jumps, and not including the first number in their count.
- Assess language by asking students to say, "____ minus ____ equals ____" after solving each problem.
- Ask students to explain how they could check that their answers are correct.
Review and closing(5 minutes)
- Ask students to pass their papers to the front.
- Call on a few students to offer insights about the most challenging subtraction problem they encountered and the strategies they used to solve the problem.
- Provide the sentence frame, "I solved the problem by ____." As students suggest strategies list them on the board.
- Tell students to give a thumbs up if they used the same strategy to solve the subtraction problems.
- Tell students to compare and contrast they way they solved the subtractions problems with a partner. If students got different answers, have them work together to self-correct errors.