16-year-old Helena Muffly wrote exactly 100 years ago today: 

Tuesday, February 6, 1912:   Am trying to get ready for monthly exams. They come tomorrow and the day after. I have sad hopes and misgivings for one study especially.

Her middle-aged granddaughter’s comments 100 years later:

I’ve recently posted many of Grandma’s diary recent entries which indicated that she was working very hard on her algebra.

And, I’ve provided a lot of background information about algebra a hundred years ago. When I got ready to write this post, I wondered what else I might write about algebra.

To get inspiration, I flipped through  a 1912 algebra textbook —and I happened to notice that one of the problems in  the book was about the average height of males and females.—and it included a data table with heights for selected ages between 3 and 21.

This reminded me that I’ve heard that on average people are taller now than they were a hundred years ago—and the next thing I knew I was headed off on a tangent.

Average Height by Age and Gender, 1912 and 2012

I found recent Centers for Disease Control data on average heights in the US.  Since 2012 data are not yet available, I assumed that it is the same as it was in recent years.  I also assumed that the data in the algebra book was correct for 1912.

On average, three-year-old children are much taller now than they were 100 years ago. Three-year-old boys are almost 4 inches taller; girls about 3 and 1/2 inches.

By age, 21,  males now are, on average, more than 1 1/2  inches taller than they were a hundred years ago. In 1912 the average 21-year-old male was 68.25 inches (5 feet 8.25 inches) tall. Now the average male in the US  is 69.9 inches (5 feet 9.9 inches)  tall.

Females are about 1/2 inch taller now than they were a hundred years ago. In 1912 the average 21-year-old female was 63 .75 inches (5 feet, 3.75 inches) tall.  Now the average 21-year-old female in the US is 64.3 inches (5 feet 4.3 inches) tall.