Lesson 5

The purpose of this Number Talk is to elicit strategies and understandings students have for subtracting 1 or 2 from a given number. Students may use the structure of the count sequence and count back to determine the difference (MP7).

• Display one expression.
• “Hagan una señal cuando tengan una respuesta y puedan explicar cómo la obtuvieron” // “Give me a signal when you have an answer and can explain how you got it.”
• 1 minute: quiet think time

• Share and record responses.
• Keep problems and work displayed.
• Repeat with each expression.

• “¿En qué se parecen los problemas 3 y 4? ¿En qué son diferentes?” // “How are problems 3 and 4 the same?  How are they different?” (They both start with 8. They are both subtraction. One subtracts 1 and the other subtracts 2. One is 7 and the other is 6.)

The purpose of this activity is for students to learn stage 2 in the center Check it Off. In this stage students subtract within 10 in any way that makes sense to them. Students may count all and remove some before counting again, count back, or use a known fact. Students are introduced to the term difference. They write subtraction expressions to represent differences. If students write an expression with the minuend and subtrahend in reversed order, for example \(4 - 7\) instead of \(7 - 4\), ask them to represent the expression with cubes or two-color counters. Students will see that if they have four cubes, they are not able to take away seven. Allow students to think about how they can write an expression that represents beginning with one of the numbers and taking away the other to find the difference. Avoid telling students that the bigger number is always first in a subtraction expression since this will not remain true when students begin working with negative numbers. 

• Each group of 2 needs a set of Number Cards 0-10.

• Groups of 2
• Give each group a set of number cards, two recording sheets, and access to two-color counters and 10-frames.
• “Vamos a aprender una nueva forma de jugar 'Márcalo'. Esta vez, en lugar de sumar para encontrar cada número en la hoja de registro, restarán” // “We are going to learn a new way to play Check it Off. This time, instead of adding to find each number on the recording sheet, you will subtract.”
• Demonstrate choosing two number cards.
• “Ahora, encuentro la diferencia entre los dos números. La diferencia es el resultado cuando se le resta un número a otro. ¿Cuál es la diferencia entre estos dos números? ¿Cómo lo saben?” // “Now I find the difference between the two numbers. The difference is the result when one number is subtracted from another. What is the difference between these two numbers? How do you know?”
• Demonstrate checking off the number on the recording sheet.
• “Después de marcar el número, escriban una expresión de resta para mostrar la diferencia” // “After you check off the number, write a subtraction expression to show the difference.”
• Demonstrate writing the subtraction expression.
• “Sigan turnándose con su compañero. La persona que marque más números gana” // “Continue taking turns with your partner. The person who checks off the most numbers wins.”

• 15 minutes: partner work time
• As students work, consider asking:
  • “¿Cómo encontraron la diferencia?” // “How did you find the difference?”
  • “¿Qué expresión escribieron?” // “Which expression did you write?”
• Monitor for students who count out counters, remove some and count again or count back to find the difference.

• “Tengo los números 7 y 3. ¿Cómo puedo encontrar la diferencia?” // “I have the numbers 7 and 3. How can I find the difference?”
• Invite previously identified students to share.
• “¿Qué expresión de resta puedo escribir para mostrar la diferencia?” // “What subtraction expression can I write to show the difference?”

The purpose of this activity is for students to choose from activities that focus on counting up to 20 objects or adding and subtracting within 10. Students choose from any stage of previously introduced centers and are encouraged to choose the center that will be most helpful for them at this time. 

• Counting Collections
• Number Race
• Check it Off
• Five in a Row: Addition and Subtraction

• Gather materials from previous centers:
  • Counting Collections, Stage 1
  • Number Race, Stage 3
  • Check it Off, Stages 1 and 2
  • Five in a Row: Addition and Subtraction, Stages 1 and 2

• Groups of 2
• “Ahora van a escoger centros de los que ya conocemos” // “Now you are going to choose from centers we have already learned.”
• Display the center choices in the student book.
• “Piensen qué les gustaría hacer primero” // “Think about what you would like to do first.”
• 30 seconds: quiet think time

• Invite students to work at the center of their choice. 
• 8 minutes: center work time
• “Escojan qué les gustaría hacer ahora” // “Choose what you would like to do next.”
• 8 minutes: center work time

• “Hemos jugado muchos juegos con suma y resta. Mencionen algo en lo que hayan mejorado por haber jugado estos juegos” // “We have been playing lots of games with addition and subtraction. What is something you have gotten better at from playing these games?”