## Lesson: Keeping Track of and Displaying Data Introducing the Concept

Last year, students represented and compared data using tally marks. Begin with this concept to reinforce the idea that each tally mark stands for one piece of data that is collected. The connection between tally marks and summarizing data can then be shown visually.

Materials: chalkboard

Preparation: none

Prerequisite Skills and Concepts: Students should have basic counting skills and be able to skip-count by fives. Students should be able to make tally marks and interpret data.

Write the months of the year in large letters on the chalkboard.

• Say: Today we will make a tally chart of the birthdays in our class. It will show the month of each person's birthday. I need a volunteer to record the tally marks.
Choose a volunteer to write one tally mark next to the month that is announced by each student.
• Ask: In which month is your birthday?
Ask each student the same question. As the volunteer records the tallies, students should realize that each student is receiving their own tally mark on the board. This is crucial to understanding that each tally mark represents an individual's birthday.
• Ask: How can we show tally marks so they will be easier to count later?
Have volunteers offer ways to show tallies for easier counting. Lead students to recommend that every fifth tally be a slash through the first four existing tallies. This offers an easy method for skip-counting by fives.

Continue questioning each student until all birthday months are recorded. Allow time for the class to study the tally chart.

• Ask: How many students are present today? Please count the total number of students in class today.
Students should respond with the correct number of students in the class.
• Ask: How many tally marks should be on the board?
Students should realize that the number of tally marks should be the same as the number of students in the class. If the numbers do not match, find and correct the problem.
• Ask: How did you count the tallies?
Students should realize they can skip-count by fives for the tallies with diagonals. Then they can count up by ones for the single tallies left on the board.
• Ask: What conclusions can you draw just by looking at the tally chart on the board?
Allow enough time for students to draw at least one conclusion. Write each conclusion on the board. Conclusions can include the following: most popular month for birthdays, least popular month for birthdays, months with no birthdays, comparison of tallies for two or more months.

Make a copy of the tally chart on a sheet of paper. You may use it later to demonstrate how to create a bar graph or line plot from existing data.