Thankfully none of those other items have ever been in my life.
It's still illegal unless you're 21 or over, so I'm not really sure why that would make your job as a high school teacher any more difficult.
I've been teaching 21 years and I can tell when a student has started smoking pot. When a young person begins smoking their grades usually drop and they do not seem to care. This may not be the case with adults, but it is VERY obvious when working with youth.
It's also easy to believe there are students where you don't notice.
Heck, these kids shouldn't be drinking coffee or caffeinated soda, either.
http://www.livescience.com/37889-marijuana-users-lack-motiva...
Sure, if a student has problems from it you will be able to observe that, but it's flawed reasoning to go from "I observe some students having problems" to "Using always leads to those problems".
And I don't naively believe that marijuana is harmless, but if you give me a choice between prohibition for everyone and (further support for) programs that reach out to students that exhibit sudden changes in behavior, it isn't very hard to decide.
We lead the nation in welfare, alcohol abuse and fetal alcohol effects, suicide, sexually transmitted disease, credit card debt, number of women murdered, and domestic abuse.
Now we are all going to be high as a kite, too.
This does not make my job any easier.