Display the class number line (0–130) where students can see and reach it with a pointer.

Attach a desk number line (0–100) to each student’s desk to use throughout the year.

Display the Math Practices page where all students can see it.

Gather and assemble two-pan balances. See Lesson 1 Materials Preparation.

Gather collections of objects that vary by mass: steel spheres, glass spheres, wood spheres, connecting cubes, and other found objects.

Gather small objects each with a mass less than 100 grams. See Lesson 4 Materials Preparation.

Gather objects each with a mass of about 100 grams. See Lesson 4 Materials Preparation.

Gather sets of standard gram masses (one 100-g, two 50-g, ten 20-g, ten 10-g, fifteen 5-g, twenty 1-g masses) for each student pair. See Lesson 3 Materials Preparation.

Gather a large marshmallow or cotton ball.

Have the following tools readily available for the Daily Practice and Problems items in this unit.

• You and your students will need:
  

  Triangle Flash Cards: Group F (Teacher Guide)
  Addition Facts I Know chart
  200 Chart (Student Activity Book) Reference
  Addition Strategies Menu (Student Activity Book) Reference
  Subtraction Strategies Menu (Student Activity Book) Reference
  connecting cubes
  base-ten pieces
  individual clocks
  number lines
  centimeter/inch rulers
  coin jars and coins from Unit 1 Lesson 1
  a collection of coins (pennies, nickels, dimes, and quarters)
  

• You will also need:
  monthly calendar
  demonstration clock
  

LESSON	SESSIONS	DESCRIPTION	SUPPLIES
LESSON 1 Compare and Order Masses	2	Students compare masses with a two-pan balance and put them in order from largest to smallest mass. By experimenting with the objects, students probe some basic questions about mass.	two-pan balances clay one-inch wood spheres one-inch glass spheres half-inch steel spheres connecting cubes small containers
LESSON 2 The Mouse-Proof Shelf	1–2	In the Adventure Book story, “The Mouse-Proof Shelf,” four mice apply what they have learned about mass to balance a tilting lamp. The students find combinations of mass that will balance pairs of mice.	connecting cubes two-pan balances
LESSON 3 Balanced and Equal	1–2	Students use two-pan balances and 1-, 5-, 10-, 20-, 50-, and 100-gram masses to practice composing and decomposing numbers. Through this process, they recognize that different partitions of a number have the same total because the pans balance. Students then apply the commutative and associative properties of addition to write number sentences that represent mass.	two-pan balances standard gram mass sets
LESSON 4 Measuring Mass	3	Throughout the lab, students compose and decompose numbers, compare quantities, apply properties of addition, and solve addition and subtraction problems involving mass.	two-pan balance objects less than 100 grams each objects approximately 100 grams each standard gram mass sets number lines large marshmallows or cotton balls
LESSON 5 Compute with Mass	2	Students practice adding two-digit numbers in the context of mass. They play the Make 99 Game in which they practice adding one-digit numbers to two-digit numbers.	standard gram mass sets two-pan balance envelopes
LESSON 6 Elapsed Time	2	Students continue to practice telling time to the nearest five minutes. They also solve elapsed-time problems involving time measurements to the nearest five minutes. The book A Second is a Hiccup by Hazel Hutchins is read aloud to help students understand different lengths of time.	individual clocks demonstration clock number lines A Second is a Hiccup by Hazel Hutchins