It may seem that the goal of banning nicotine and tobacco use in schools is to prevent young people from using cigarettes in their teens, but this is not the goal because young people who want to use these products outside schools. What schools aim at with this ban is to prevent non-smoking students from becoming second-hand smokers.
Passive smokers are those who do not smoke but live with smokers and end up ingesting cigarette smoke that is as toxic and harmful as the cigarette itself.
It's based on opinion, but I would put that they won't start and get an addiction at an early age so it will be more difficult for them to start later in life.
The main function of the kidney is the excretion of body wastes and harmful chemicals into the urine. The nephron is the functional unit of the kidney responsible for excretion.