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Lesson excerpt:

NC Mathematics Standard(s):

Operations and Algebraic Thinking

NC.2.OA.4 Use addition to find the total number of objects arranged in rectangular arrays with up to 5 rows and 5 columns; write an equation to express the total as a sum of equal addends.

Standards for Mathematical Practice:

1.      Make sense of problems and persevere in solving them.

      4.   Model with mathematics.

      6.   Attend to precision.

      8.   Look for and express regularity in repeated reasoning.

Student Outcomes:

●     I can use addition to help me figure out how many objects are in an array.

●     I can write a number sentence to show the total number of objects that are in an array.

Math Language:

●       add

●       row

●       column

●       array

●       equation

●       sum

●       equal

Materials:

●     examples or pictures of things/foods that are packaged in trays (ex. egg carton, box of chocolates, tray of cookies)

●     blank white paper

●     grid paper

●     rulers

●     pencils

●     scissors

●     bags of counters (red/yellow circle counters, Unfix cubes etc.)

Advance Preparation:

●     Count out counters for bags. Each bag will contain counters that can easily be arranged in rows and columns.  Examples: 12, 15, 16, 18, 20, 24, 25 

●     Gather pictures or examples of packaged items

Launch:

(5 minutes)

Think about things that are packaged in trays. Show examples: eggs, chocolates, cookies, muffins, etc.

1. What do you notice about the trays?

2. Are there an even or odd number of items displayed? How do you know?

3. What are columns and rows?

4. Have you ever heard of the word array?

5. How can you count items in an array?

Explore:

Designing Your Trays (20 minutes)

Students will work with a partner.  Pass out the bags of counters and a sheet of paper to each partnership.  More than one partnership can have the same amount of counters in a bag.  Students may think of the counters as cookies or cupcakes. Their job is to design a tray to package the items.  Instruct partners to empty their bag of counters and begin putting items in rows and columns.  Are there several ways to arrange your items in rows and columns? Using the piece of blank paper, students design and draw the trays to package their counters.  As you walk around the classroom observing the work of the partners, listen for the vocabulary that they are using.  How are they arranging the items, one long row, several columns and rows? Students then label their designs with an equation that matches. Examples of drawings:

12 counters                                                                                            

3+3+3+3=12

4+4+4=12

As you walk around the room, think about the mathematics you want to highlight in the discussion.  Which partnerships would you like to share and in which order.  Encourage partners to think of as many ways as they can to arrange the items in a tray.  Example: 12 (12x1, 3x4, 4x3, 2x6, 6x2)

Discuss:

Share Your Designs (20 minutes)

Gather all students together as a group to be an audience. Call partners to share their designs.  Ask partners what strategies they used to arrange the counters.  Does the equation you wrote match the model? What is the sum?  What strategy did you use to add all the numbers?  Can the audience of students think of additional tray designs for that particular number of counters?