Typically, nineteenth-century students played games and socialized outside the school in the morning. Unless the school had a bell tower, the teacher would stand at the door and ring a hand bell when it was time for school to commence in the morning or after a recess. Students needed to be within earshot to hear the bell, or otherwise risk punishment for tardiness.
Today most schools have a systematized bell that rings at the beginning and end of school as well as between class periods. Such a system brings uniformity to class period lengths in schools where students travel to different classrooms throughout the day. Teachers tailor their lessons to adhere to the exact class period allotments. Consequently, such a system does not allow for any deviation-classes must end, regardless of the value of what is happening in the classroom at the moment the bell rings.
Then & Now: