Lesson 21

The purpose of this Number Talk is to elicit strategies and understandings students have about the relationship between addition and subtraction. Each addition and subtraction equation represents the same part-whole relationship. These understandings help students develop fluency and will be helpful later in this lesson when students solve missing addend problems.

• 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

• Record answers and strategy.
• Keep expressions and work displayed.
• Repeat with each expression. 

• “¿Cómo les puede ayudar encontrar el valor desconocido en la primera ecuación a resolver la segunda ecuación?” // “How can finding the missing value in the first equation help you with the second equation?" (I know that 1 more than 4 is 5, so I also know that 1 less than 5 is 4.)

The purpose of this activity is for students to learn a new center called Number Puzzles. Students use number cards to fill in addition and subtraction equations up to 10 on a game board. The missing values are in different places in the equations and each number card may only be used once. Students build fluency for addition and subtraction within 10.

• Create a set of Number Puzzles Cards from the blackline master for each group of 2.

• Groups of 2
• Give each group a set of cards and a game board.
• “Vamos a conocer un nuevo centro llamado 'Acertijos numéricos'” // “We are going to learn a new center called Number Puzzles.”
• Display a game board.
• “Necesito poner mis tarjetas de números de modo que cada ecuación sea verdadera. Puedo usar solo una vez cada tarjeta de números” // “I need to place my number cards so that every equation is true. I can only use each number card once.”
• “Intentemos algunas juntos. Observen la primera ecuación. ¿Qué tarjetas de números podría poner en el tablero para que la ecuación sea verdadera?” // “Let’s try some together. Look at the first equation. What number cards could I put on the board to make the equation true?”
• 30 seconds: quiet think time
• 1 minute: partner discussion
• Share responses.
• Repeat 1–2 more times, as needed.

• “Usen sus tarjetas de números para jugar este juego. Completen un acertijo antes de pasar al siguiente. Terminen tantos como puedan” // “Use your number cards to play the game. Complete a puzzle before moving to the next one. Finish as many as you can.” 
• 10 minutes: partner work time 

• “¿Qué métodos usaron para asegurarse de poner cada número en el lugar correcto?” // "What methods did you use to make sure you were putting each number in the right place?"

The purpose of this activity is for students to choose from activities that offer practice adding and subtracting within 10. Students choose from any stage of previously introduced centers.

• Capture Squares
• Math Stories
• What’s Behind My Back

• Gather materials from previous centers:
  • Capture Squares, Stages 1 and 2
  • Math Stories, Stage 4
  • What's Behind My Back, Stage 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. 
• 10 minutes: center work time
• “Escojan qué quieren hacer ahora” // “Choose what you would like to do next.”
• 10 minutes: center work time

• “Cuéntenle a su compañero cuál es su cosa favorita cuando trabajan en los centros y por qué es su favorita” // “Tell your partner your favorite thing about center time and why it is your favorite.”