The purpose of this activity is for students to learn Stage 2 of the What’s Behind My Back? center. Students snap a tower of 10 cubes into two parts and hide one part behind their back. Then their partner determines how many connecting cubes are hidden. Students may use connecting cubes, 10-frames and counters, fingers, or drawings to figure out how many connecting cubes are hidden. As they choose a strategy, they use appropriate tools strategically (MP5). Monitor for students who:

• Create another tower of 10 connecting cubes, snap it into two pieces to show the cubes that are showing, and then count the rest of the cubes to determine how many cubes are hidden.
• Hold up the same number of fingers as the number of connecting cubes that are showing and count the number of fingers that are down to determine how many connecting cubes are hidden.
• Place counters on a 10-frame to represent the connecting cubes that are showing and count the empty squares to determine how many connecting cubes are hidden.

• Select previously identified students to share.
• “¿Cómo les ayudó hacer otra torre de 10 cubos a averiguar cuántos cubos estaban escondidos?” // “How did making another tower of 10 cubes help you figure out how many cubes were hidden?”
• “¿Cómo les ayudaron sus dedos a averiguar cuántos cubos estaban escondidos?” // “How did your fingers help you figure out how many cubes were hidden?”
• “¿Cómo les ayudó poner fichas en el tablero de 10 a averiguar cuántos cubos estaban escondidos?” // “How did putting counters on the 10-frame help you figure out how many cubes were hidden?”

The purpose of this activity is for students to determine how many are needed to make 10 when added to a given number. This activity is presented as the same context as the first activity, except students are not shown the visual of the cubes. Because the context is connecting cubes, one way to determine how many cubes are hidden is to create and snap a tower of 10 cubes. Students may also use their fingers or put counters on a 10-frame. As they choose a strategy, they reason abstractly and quantitatively (MP2) and they may choose to use appropriate tools strategically (MP5).

• Invite students who built towers of connecting cubes to show how they figured out how many cubes were hidden.
• Display a 10-frame with 4 red counters and 6 yellow counters. Display a tower of 10 connecting cubes broken into 4 and 6:

  

  

• “¿En qué se parece formar 10 con cubos encajables a formar 10 con un tablero de 10?” // “How is making 10 with connecting cubes the same as using a 10-frame?” (I get the same combinations of numbers to make 10. 4 connecting cubes and 6 connecting cubes make 10, just like with counters.)

The purpose of this activity is for students to choose from activities that offer practice with counting, adding, composing, and decomposing numbers.

Students choose from any previously introduced stage from these centers:

• What’s Behind My Back?
• Math Fingers
• Shake and Spill
• Counting Collections
• Roll and Add

• Display a tower of 10 cubes, snapped into 9 cubes and 1 cube.

  

• “¿Cuáles son las partes que Elena encontró que forman 10?” // “What are the parts that make 10 that Elena found?” (9 and 1)
• “¿Qué ecuación puede escribir Elena?” // “What equation can Elena write?” ()