If you think about it, they have numerous classroom interruptions, lunch, recess, time spent going to and from different classrooms, etc. My children usually enjoy the afternoons playing with the other homeschooled kids in the neighborhood who have also finished their work. Mom gets to catch up on housework. There are so many benefits to homeschooling. If your child is working on an assignment, he doesnt have to stop because the clock says so or because the bell rings.
Children can work at their own pace and at their own level.
If they are ready to advance, they dont have to wait for the rest of the class to catch up. And of course you dont have hours of homework each evening. If you are seriously considering homeschooling, my advice is to do a lot of research beforehand. I spent a year reading every book I could find and surfing the net for information. You dont have to be a rocket scientist to homeschool.