Back-to-school: Many Pennsylvania schools have been in session for more than week, and NY schools have now seen their students return as well. Now that we can all take a deep breath after the chaos that is back-to-school, we have time to look at some interesting facts about the United States and education.

The average backpack weighs 20% of the student’s body weight. The recommendation to teachers, however, is to help students keep that weight to around 10%.

That can be tough when teachers across the U.S. are dealing with 33 million elementary school children, 17 million kids in high school and a little over eight million pre-school age students. When you factor in college students, there are about 78 million students that participate in the back to school madness.

Take that number and then consider, there are only 8 million teachers in the U.S., set to handle all of those students.

When it comes to back to school shopping, parents aren’t fans of shelling out hundreds for supplies. Of those supplies, the most dreaded purchases are textbooks, but they are closely followed by clothing and electronics as the items parents would rather not have to buy.

Most children, around two-thirds, roughly, like school. However, for a small percentage (2.4% to be exact), Didaskaleinophobia sets in. This means an acute fear of going to school.

For those who still use the wooden pencils, they can plan on sharpening their writing tool an average of 17 times and writing about 45,000 words — or drawing a 35-mile long line — before that pencil has to be tossed and replaced.

Pencils can be used anywhere — from the school desk to zero gravity to underwater. Before erasers were invented, the most common way to remove mistakes was by using a balled up piece of white bread.

Finally, an interesting fact. Prior to the Depression, school ended with the eighth grade. However, because of the Depression, high school was created to keep youth from competing for the limited number of jobs available and ensure that adults and family men were employed. Today, about 52% of high school students work part-time and 20% report working full-time.