For one thing, it's the law. If you didn't go, your parents could be in big trouble.
But there are other reasons kids in the U.S. -- and most other countries -- are required to attend school until they reach a certain age.
For one thing, a healthy democracy depends on people who are informed about issues. Citizens vote, and they take part in other civic duties -- educated people are likely to make better choices.
The more education someone has, the more money he is likely to make during his life. And being in school helps you learn how to deal with others, set goals and get things done. Those are important skills.
Requiring kids to go to school is called "compulsory education." (Compulsory means that you have to do something.) But American kids didn't always have to attend. In fact, only wealthy people went to school until the 1840s.
A Massachusetts official named Horace Mann led a movement to change that, and by 1900 free elementary school was available to American children.
The U.S. Education Department says that in 1869-70, the average number of days each student attended was 78. By 1900, it was 144 days, and by 1950, it was 178.
Kids got the summer off from school because schools, in earlier times, followed a farmer's schedule. That allowed kids to help bring in the summer harvest. That tradition stuck.
Today kids in most states are required to go to school for 180 days each academic year. That allows for four nine-week periods of 45 days or two 90-day semesters.
But beware: Some educators think kids should be in school a lot longer.
Some schools have raised the number of required school days, and some folks think that sometime soon, 200 days will be the magic number -- so enjoy 180 while you can!