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Baby Weight

  • Lesson
Number and OperationsData Analysis and Probability
Location: Unknown

In this lesson, students work with data to complete an organized chart by doubling or halving numbers. Then, they compare data using vertical and horizontal bar graphs.

Begin a class discussion about what it means to double or halve numbers. Ask students to give some examples of doubling or halving (e.g. half of 4 is 2; double 10 is 20; and so on). Ask students to share some situations in which they would double or halve numbers (e.g. baking, making groups, etc.).

Bring a group of students up to the front of the room, such as 5 students, and ask them how they would double the size of the group. Each student can pick another student to join the group at the front of the room.

Next, bring a group of an even number of students to the front of the room. Tell them to halve the group. Send the group back to their seats.

Distribute the Baby Weight Activity Sheet to each student.

pdficon Baby Weight Activity Sheet 

Discuss the "rule of thumb" as stated on the activity sheet: A baby doubles its weight in six months. Complete the first two rows as a class. Give students time to complete the rest of the chart individually.

750 babies

Using a red crayon for the birth weights and a brown crayon for the six-month weights, explain how to complete the bar graph. Students should pair up and compare their bar graphs. The teacher can circulate throughout the room to check for accuracy.

You may wish to have students create additional bar graphs for other babies, similar to the ones in questions 2 and 3 on the activity sheet using grid paper.

pdficonGrid Paper

Solutions to the Baby Weight Activity Sheet 

The following are the missing numbers from the chart (question 1):

Amy 10
Benito 8
Cathy 18
Demetrius 16
Erik 14
Fran 6
Greg 5

As a class, discuss the similarities and differences between the two graphs completed (questions 2 and 3 on the activity sheet.) Students may point out that both graphs are bar graphs and show a comparison between birth weight and six-month weight. Students may also say that the graphs show the weights of different babies and the fact that they "look" different (one is horizontal and one is vertical).


  • Parker, Tom. Rules of Thumb. 2 vols. Boston: Houghton Mifflin Co., 1983, 1987.
  • Cook, Marcy. "IDEAS: Applications." The Arithmetic Teacher. Vol. 36, No. 8, April 1989, pp. 27-32.

Assessment Options 

  1. Use the Baby Weight Activity Sheet to check for student comprehension.
  2. As an exit slip, have students write their favorite number at the top of an index card folded in half (length wise). Ask students write half and double their number on the left and right side of the index card, respectively.  
  3. Ask students to share a type of scenario that would require them to halve (or double).


  1. Students can order the students' weight at birth from least to greatest. [Solution: Amy, Fran, Erik, Benito and Demetrius tied, Cathy, Greg]
  2. Students can find out (from their parents) their birth weights and weight at six months to determine if these weights follow the rule of thumb as discussed in class.

Questions for Students 

1. When would you need to halve a number?

[Answers will vary. Sample: I would need to halve a number if I were splitting candy with my brother fairly.]

2. Provide an example of when you would need to double a number.

[Answers will vary. Sample: If a recipe makes enough cookies for four, but you have eight people coming over.]

3. Assume that Amy's parents told her she weight 6 lbs. at birth. How much did she weight six months later?

[12 lbs.]

Teacher Reflection

  • How could you differentiate the lesson to help struggling students?
  • How could you change the lesson plan to help students see that halving and doubling are inverse operations?
  • How were you able to discern whether or not the bar graphs helped students see the relationship between halving and doubling?

Learning Objectives

Students will:
  • Complete a chart by doubling or halving numbers.
  • Compare data by use of vertical and horizontal bar graphs.

NCTM Standards and Expectations

  • Connect number words and numerals to the quantities they represent, using various physical models and representations.
  • Count with understanding and recognize "how many" in sets of objects.
  • Develop a sense of whole numbers and represent and use them in flexible ways, including relating, composing, and decomposing numbers.
  • Develop understanding of the relative position and magnitude of whole numbers and of ordinal and cardinal numbers and their connections.
  • Pose questions and gather data about themselves and their surroundings.

Common Core State Standards – Mathematics

Grade 1, Measurement & Data

  • CCSS.Math.Content.1.MD.C.4
    Organize, represent, and interpret data with up to three categories; ask and answer questions about the total number of data points, how many in each category, and how many more or less are in one category than in another.

Grade 2, Measurement & Data

  • CCSS.Math.Content.2.MD.D.10
    Draw a picture graph and a bar graph (with single-unit scale) to represent a data set with up to four categories. Solve simple put-together, take-apart, and compare problems using information presented in a bar graph.