options: Ratios & Proportional Relationships: students learn to recognize, describe, represent, and reason with ratios, rates, proportional relationships, and percent.

Measurement & Data: students learn to work with data and measure attributes such as time, money, length, area, and volume. They may learn to compare measurements to operations and convert between different units of measure.

Statistics & Probability: students learn to analyze and produce data distributions, and build understanding of univariate and bivariate data. They learn to interpret data, make statistical inferences, justify conclusions, understand rules of probability, and use probability to make decisions.

Functions: students learn to define, use, and evaluate functions to model relationships between quantities.

Counting & Cardinality: students learn to know number names and the count sequence, count to tell the number of objects, and compare numbers.

Geometry: students learn to classify geometric figures by their properties, and understand and compare the relationships between them. Students develop and use formulas to compute lengths, areas, and volumes, and they use transformations to generate new shapes and compare existing ones. Geometry can be studied with and without coordinates.

Number & Operations - Fractions: students learn to understand fractions as numbers and may work with them using addition, subtraction, multiplication, and division.

Number Systems and Quantity: students learn to understand the complex number system and reason quantitatively.

Operations & Algebra: students learn to solve problems using algebraic thinking and operations such as addition, subtraction, multiplication, and division. They may learn to identify and explain arithmetic patterns, evaluate or manipulate numerical expressions, and reason with equations and inequalities.

Number & Operations in Base Ten: students learn to work with the base-ten system and build place value understanding.

Modeling: students learn to choose and use appropriate mathematics and statistics to analyze real-world empirical situations, improve decisions, and report on their conclusions and the reasoning behind them.
problem_activity: Narrative
The purpose of this activity is for students to revisit stage 2 of the What's Behind My Back center, which was first introduced in grade 1. Students begin with a tower of 10 connecting cubes. They break apart the tower and represent the two parts with a drawing and an expression. Throughout the activity, students practice using what they know about sums of 10 and the relationship between addition and subtraction to find unknown addends. Students explain their reasoning about how they know how many cubes are missing to their partner (MP3). As students discuss, listen for the ways students show how they are looking for and using the counting sequence, properties of operations, or the relationship between addition and subtraction (MP7).
MLR8 Discussion Supports.
Make connections between representations visible. Think aloud, use gestures and a labeled display to show connections between parts of the equation and the cubes that are visible and those that are hidden.
Advances: Listening, Representing
Required Materials
Materials to Gather
Connecting cubes
Materials to Copy
What's Behind My Back Stage 2 Recording Sheet Grade 1
Required Preparation
Gather a tower of 10 connecting cubes to use in the launch.
Launch
Groups of 2
Give each group 10 connecting cubes.
“We are going to play a game you may have played in first grade called What’s Behind My Back?”
Show students a tower of 10 cubes. Put the tower behind your back. Break off 4 cubes, and display the rest of the tower.
“How many cubes are behind my back? How do you know?” (4 because there are 6 and 4 more makes 10. I know because
\(10 - 4 = 6\)
.)
30 seconds: quiet think time
1 minute: partner discussion
Share responses.
“After one partner has hidden the cubes, switch roles.”
Activity
10 minutes: partner work time
Activity Synthesis
Ask a student to play a round of the game with the class.
As the student displays the tower, write the related addition equation with an unknown addend on the board. (for example, if a student shows 2 blocks, write
\(2+\underline{\hspace{.5 cm}}=10\)
.)
“How does this equation represent the game?”
“What number makes the equation true?”
“How can we represent the game with a subtraction equation?” (
\(10 - 2 = 8\)
or
\(10 - 8 = 2\)
)
If needed, ask students to show how the numbers in the addition and subtraction equations represent the cubes in the round.


correct_option_index: 8