Today’s Wonder of the Day was inspired by Katie. Katie Wonders, “Why are there 12 grades for school?” Thanks for WONDERing with us, Katie!

Wake up, Wonder Friends! It's time for school! You don't want to be late. Whether you're in elementary, middle, or high school, it's time to get busy learning.

Most kids, at one time or another, look forward to the day when they'll be done with school and can go on to college or trade school or enter the workforce. When you're a kid, though, your job IS school.

You usually start out in kindergarten around age five. Then you proceed to first grade and, year after year, the numbers keep adding up. Finally, one day, you begin twelfth grade. That means you're a senior in high school and just one year away from graduating.

Have you ever WONDERed about why it is that you have to make your way through 12 grades? If you count kindergarten, that's 13 years of elementary, middle, and high school. Why not 14 years? Or only 10 years?

Public school in the United States has a long and interesting history. Today's students enjoy technology-filled classrooms led by dedicated teachers. It's probably hard for most kids today to imagine that only 150 years ago there were many places across the country without any form of public education.

The settlers in the original 13 colonies placed a high value on education. However, most of them educated their children at home. The Puritans were the first to push for some form of public education, and they began to establish some of the first schools.

Although Thomas Jefferson early on suggested a nationwide educational system funded by tax dollars, his idea did not catch on until nearly a century later. Thanks to an education crusader named Horace Mann, Massachusetts became the first state with compulsory school laws in 1852.

Mann also led the charge to change schools from a one-room schoolhouse that taught all children together to a multilevel format that separated children into separate grades by age. Mann's "age grading" system proved to be very successful and soon became the model for other public school systems around the country.

Thanks to Mann and other education crusaders, public school systems slowly began to develop nationwide. However, it was not until 1918 that all children in the U.S. were required to attend at least elementary school.

Another battle that had to be fought was for equal access to school for all children, regardless of race. In the early 1900s, many schools were segregated by race. It was not until 1954 that the Supreme Court decided the case of Brown v. Board of Education, which finally guaranteed public school access to children of all races.

Up until the second half of the 19th century, elementary education was the primary focus of public school systems. At that time, agriculture was still the driving force of the economy and many people felt that a basic elementary school education was sufficient for children who were needed to work on farms.

As the country began to industrialize, however, higher education began to play a more important role. Children weren't needed as much on farms and were too young to work in factories. Plus, they needed advanced education to prepare them for jobs that were more skilled and technological.

Over time, public school systems settled into the 13-year course of elementary, middle, and high school that we have today. The exact reasons for having kindergarten followed by grades one through 12 are not clearly known.

Most people, however, believe it's a natural result of the child development cycle. Kindergarten begins around age five, which is the age at which most children are able to sit still and listen in order to learn. School continues until grade 12, at which point most children are 18 by the time they graduate. For most purposes, the age of 18 is considered the beginning of adulthood, which is a natural time for young adults to graduate and make their own way in the world.

Wonder What's Next?

Tomorrow’s Wonder of the Day takes a closer look at the skin we’re in!