Another reason is they might start disrupting the class and the teacher then no one else will learn.
Lastly it will teach them a lesson because when they drop out of school there going to need a job so it will teach them a lesson because they wont be able to get a good job because they didn't finish school and the people that work there are probable not going to want someone who gives up there going to want someone who are hard working and wont quit even if something is a little difficult. Then they might want to go back to school because they figured out that you cant have a good life without a good education.
So this is why I think that students should not be forced to stay in school till there 18. BY NOAH J ALLEN :) :D :P