Math Background

Lesson: Estimating and Measuring Amounts
Developing the Concept

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In this lesson, students use standard units to measure length to the half inch.

Materials: one inch-ruler (Learning Tool 24 in the Learning Tools Folder), and one copy of Worksheet A (PDF file) for each pair of students

Preparation: Distribute the rulers or have students cut out the ruler from Learning Tool 24, which shows a one-inch ruler and a centimeter ruler.

Prerequisite Skills and Concepts: Students should know how to measure to the nearest inch.

  • Ask: How many inches are shown on the ruler? (12) How many equal parts is each inch divided into? (8)
  • Say: Look at the first inch on your ruler.
  • Ask: Why do you think that one of the marks that divide the inch into equal parts is longer than the other marks?
    Students should realize that the longer mark represents one-half inch.
  • Say: Point to the mark that represents 1one-half inches. Observe students to make sure they are pointing to the correct location on their rulers. Then have them point to the marks that represent 3one-half inches, 7one-half inches, and 11one-half inches.

    Distribute Worksheet A (PDF file).

  • Say: Let's measure the length of the ribbon to the nearest one-half inch. Line up the end of your ruler with the end of the ribbon.
  • Ask: What is the length of the ribbon? (4one-half inches)
  • Say: Now measure the length of the comb to the nearest one-half inch.
  • Ask: Is the right end of the comb closer to the 3-inch mark or the 3one-half-inch mark? (the 3one-half-inch mark)
  • Ask: What is the length of the comb to the nearest one-half inch? (3one-half inches)
  • Say: Measure the length of the key to the nearest one-half inch.
  • Ask: Is the right end of the key closer to the one-half-inch mark or the 1-inch mark? (The 1-inch mark)
  • Ask: What is the length of the key to the nearest half inch? (1 inch)
  • Say: Now measure the length of the toy car to the nearest one-half inch.
  • Ask: Is the right end of the toy car closer to the 2one-half-inch mark or the 2-inch mark? (the 2-inch mark)
  • Say: Sometimes a measurement to the nearest one-half inch is a whole number.
  • Ask: What is the length of the toy car to the nearest one-half inch? (4 inches)

    Have students measure the remaining objects on the worksheet to the nearest one-half inch. (stapler: 3 inches long, toy train car: 1one-half inches long)

Wrap-Up and Assessment Hints
As students are working, remind them to line up the ruler carefully with the end of the object they are measuring. Provide students with sufficient practice reading the marks on a ruler. Assess students' ability to measure by observing them as they measure objects.


Houghton Mifflin Math Grade 3