While I agree that someone whose brain is not developed should not be using mind-altering anything, what you described is essentially puberty.
Heck, these kids shouldn't be drinking coffee or caffeinated soda, either.
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.