The following is an audio transcript of the video lesson plan Mysteries of the U.S. Pyramids.

Hi, I’m Carol, here to share the lesson Mysteries of the U.S. Pyramids. This lesson looks at the age-sex distribution of the U.S. population at six different times in history. By the end of this activity, students will be able to:

• calculate percentages using raw numbers,
• construct a population distribution graph for one point in U.S. history,
• And make connections between the shape of a population pyramid and factors that may have affected U.S. population patterns.

This activity is well-suited for high school students studying U.S. history, social studies, or math. Let’s take a closer look.

Before students can start graphing, we need to ensure that they understand population pyramids in the first place. The graph of the current world population is a great way to introduce this concept.

Population pyramids, which are also called an age-structure diagrams, are a type of histogram that displays the proportions of age and sex in a given population. On the y-axis we have ages in five-year increments. On the x-axis, we have the percentage of the total population, with the males on the left and the females on the right. You read a population pyramid by focusing on a particular bar, called a cohort, in the chart, like females, ages 30 – 34.

We can also read population pyramids by looking at the graph as a whole. The term “population pyramid” comes from its shape, which is often triangular. It’s important that students understand what trends they can identify from the shape of a population pyramid.

For example, in the global pyramid, the bars of the younger ages are wider than the bars of the older ages, so we have a population that has many more young people than older people. When a population has more young people, that population is growing, because more of the population can have children than not. Though this is a common shape for a population pyramid, not every pyramid is going to follow that trend.

To help you introduce these graphs to your students, share the world population pyramid and ask them to find where they would be represented on the graph. Have them identify the biggest or smallest age cohort, and ask them to describe what information is not displayed on the graph (like the overall number of people on the planet).

But really, the best way to get comfortable with a population pyramid is to make one! So that’s what we’re going to do.

Distribute the Student Worksheet found in the lesson plan. It has data for the raw number of people in each age cohort at six different points in time, starting with 1880. Assign each student one of the years from the Worksheet.

Their task now is to get this data ready to be graphed. Meaning, we need to convert the raw population data into the right form for us – percentages.

If you’d rather focus on other parts of the lesson, you can also give students the Answer Key to the Student Worksheet, which has all of the percentages already calculated. And allows students to move directly to graphing.

It can be helpful to model the graphing for students. You draw each horizontal bar from the center line out to the correct percentage. Rinse and repeat for each cohort.

Once the graphs are finished, it’s time to look at each time period one by one. Display one of the completed graphs from each year and use the provided discussion questions to help guide your conversation. These questions contextualize these graphs within U.S. History.

An example of one of the questions is: “Looking at the graph for 1960, there is an obvious indentation in the pyramid’s shape. Which age cohorts are these and why might that be the case? Which are the three largest cohorts that year? Why might that be the case?”

Students would look at the 1960 graph and notice that the indentation occurs in the age cohorts for people in their 20s. This is the age group that would have been born during the Great Depression. Because of the economic conditions during this time period, many fewer children were born than in other generations. Conversely, the three largest cohorts are the youngest cohorts on the graph. These represent the bulk of the Baby Boomers, a huge generation of people born during post-war prosperity.

Another question is: “Which of the graphs look most like a pyramid? What does this indicate about the population growth rate at that time?” Students will probably say 1880, with 1920 as a runner up. This would indicate that population was growing more rapidly at these times than in other times, because a larger portion of the population was in the youngest age groups.

To wrap up your discussion, have students write a short paragraph that summarizes the trends they noticed in historical and projected U.S. population growth. This works really well as an exit ticket or a refresher to start the next class.

Want to continue your exploration of population pyramids? Check out the lesson “Power of the Pyramids,” where students construct population pyramids for the current populations of different countries around the world.

Find these lessons and more fantastic activities for the classroom, at PopulationEducation.org. Thanks for watching.