standard_description: Fluently add and subtract within 20 using mental strategies. (See standard 1.OA.6 for a list of mental strategies.) By end of Grade 2, know from memory all sums of two one-digit numbers.
problem_activity: Narrative
The purpose of this activity is for students to partition rectangles to create rows and columns of equal-size squares. In the launch, students build an array with tiles and then represent it on a rectangle with tick marks as guidance. They will partition rectangles without tick marks in the next activity.
MLR2 Collect and Display.
Synthesis: Direct attention to words collected and displayed from the previous lessons. Include the word “partition.” Invite students to borrow language from the display as needed, and update it throughout the lesson.
Advances: Conversing, Reading
Required Materials
Materials to Gather
Inch tiles
Rulers
Launch
Groups of 2
Give students rulers and inch tiles.
Activity
“Use 8 tiles to make a rectangle. Your tiles should be in 2 rows.”
1 minute: independent work time
“Now, draw lines in the rectangle to show the squares. It should have the same number of equal-size squares as the rectangle you made out of tiles. You may use a ruler if it helps you.”
1 minute: independent work time
“You will draw lines to partition 2 more rectangles into equal-size squares. You can also use the tiles to build it first, if that helps.”
10 minutes: independent work time
Student Facing
Build a rectangle with 8 tiles arranged in 2 rows. Use a ruler to partition the rectangle to match the rectangle you made.
[IMG]
Use a ruler to partition the rectangle using the tick marks as a guide.
[IMG]
How many rows of equal-size squares did you make?
How many columns did you make?
Write 2 equations to represent the total number of equal-size squares.
Use a ruler to partition the rectangle using the tick marks as a guide.
[IMG]
How many rows of equal-size squares did you make?
How many columns did you make?
Write 2 equations to represent the total number of equal-size squares.
Student Response
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Advancing Student Thinking
If students create equations that match the total number of squares, but do not represent the sum of squares in each row or the sum of squares in each column, consider asking:
“How does your equation match the array?”
“Can you write an equation with equal addends that shows the sum of each row or column?”
Activity Synthesis
Invite 1
–
2 students to share their rectangles and equations for their rectangle with 3 rows and 5 columns. (
\(3 + 3 + 3 + 3 + 3 = 15\)
or
\(5 + 5 + 5 = 15\)
)
Draw a rectangle and partition to show:
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“How is this partition different from what we did in this activity?” (The squares aren’t the same size and the last column has 4 not 3.)


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