depends on how much you smoke so if you smoke every day be 30days before your clean....and drug testing in school is such bullshit..i would never attend a school that would drug test id rather go to a public school where im not getting my piss tested....but i understand if you get in major trouble mebe a piss test but still it should be up to the fucking parents not the school i think its a invasion of privacy so fuck em why do they need to worry anyways as long as they get thier money.....money talks bullshit runs a marathon