Lesson objective: Understand that milliliters and liters are used to measure liquid volumes.

Students bring prior knowledge of measuring with inches and feet from Grade 2 Unit 2, 2.MD.A.1, and Grade 2 Unit 3, 2.NBT.B.7. This prior knowledge is extended to making representations and drawings to solve one-step situational problems involving addition and subtraction of liquid volumes as students add amounts of milliliters to make a liter. A conceptual challenge students may encounter is representing larger numbers on a number line accurately and calculating with numbers up to 1,000.

The concept is developed through work with a number line, which supports the ability to read a liter cylinder scale.

This work helps students deepen their understanding of operations because the students need to use addition and subtraction to solve the problems. Also, the students understand the equivalence of 1,000 milliliters to 1 liter.

Students engage in Mathematical Practice 1 (Make sense of problems and persevere in solving them) as they use a number line and number equation to show their methods of adding milliliters to make 1 liter.

**Key vocabulary:**

- liter graduated cylinder
- liter ( L)
- liquid volume
- milliliter (ml)

**Special materials needed:**

- liter graduated cylinder
- liquid volume bottles - liter bottle of water, 500 ml bottle of water
- rain gauge