First we go through a normal traffic school and then Online Traffic School.

Traffic school is typically an eight hour course held in a courtroom or classroom on one day. The course may however, be split into shorter sessions spread over a number of days. The total "in class" time is the same either way and must equal eight hours. The typical traffic school course consists of several lectures about the traffic laws and driving safety habits as printed in the DMV driver manual.
Online traffic school refers to a Traffic School course that is completed over the Internet. online traffic school allows the student to complete the course on his own time and at his own pace.So, In this way the major difference between Traffic School and Online Traffic School is that Traffic school course held in a courtroom or classroom for a defined period at a particular place and timings are fixed means if you are late to reach the class you will miss lectures but online traffic school courses are completely online and you can start and finis your courses according to your schedule whatever is convenient to you unlike a normal traffic school.