Lesson objective: Understand that symbols may be used in an equation to represent a missing number.

Students bring prior knowledge of unknown numbers in equations from Grade 1, Unit 9, 1.OA.A.1. This prior knowledge is extended to include the use of symbols as students determine unknown numbers to create true equations. A conceptual challenge students may encounter is the use of symbols to represent unknown numbers.

The concept is developed through work with counters, connecting cubes, and ten frames, which allow students a visual representation and method of organizing the numbers they are working with.

This work helps students deepen their understanding of equivalence because students will be comparing values on each side of the equals sign to determine what number will make the equation true.

Students engage in Mathematical Practice #4 (model with mathematics) as they determine the meaning and value of symbols and use addition strategies to justify their reasoning.

**Key vocabulary:**

- determine
- equation
- true
- unknown

**Special materials needed:**

- counters
- cubes
- ten frames