Lesson objective: Writing equations to show that an even whole number is the sum of two equal addends.

Students bring prior knowledge of decomposing whole numbers from Grade 1, Unit 6, 1.OA.C.6 and Grade Kindergarten, Unit 10, K.OA.3. This prior knowledge is extended to connecting decomposing whole numbers to equations as students write equations to show that an even whole number is the sum of two equal addends. A conceptual challenge students may encounter is understanding that the addends individually do not determine whether a whole number is even or odd, i.e., 3 + 3 = 6, but you do not say six is odd because three is odd.

Throughout the lesson, students will extend this knowledge to include decomposing whole numbers up to 20 and writing a corresponding equation.

The concept is developed through work with drawing tower pairs to decompose whole numbers and writing an equation to show that an even whole number is the sum of two equal addends, which supports the development of recognizing even and odd whole numbers.

This work helps students deepen their understanding of equivalence because students will make a visual picture to match their equation showing that an even number is the sum of two equal addends.

Students engage in Mathematical Practice 4 (Model with mathematics) as they apply what they know about decomposing whole numbers to drawing tower pairs and writing corresponding equations to represent even numbers. Students also engage in Mathematical Pracice 7 (Look for and make use of structure) as they write equations to represent even numbers.

**Key vocabulary:**

- addend
- equal
- equation
- even
- odd
- sum

**Special materials needed:**

- connecting cubes (for students who need to build and model the towers before drawing them)