I went to school back before things like standardized testing and drug screening and security guards. I could pretty much come and go from the building whenever I wanted during the school day, as long as I avoided a few of the more zealous teachers. One or two of them would take it upon themselves to roam around and try to bust people.
We would smoke in the bathrooms between every class, and this one teacher would actually fucking begin sprinting from his class when the bell rang to run and catch us in the bathroom closest to his class. We would always get in there first and light up and hotbox for a few seconds, then throw the butt in the toilet.
There was a rule in our school district that you had to actually be caught with the cigarette in your hand to be suspended for it. He would be so pissed as we grinned at him through clouds of smoke, with one butt floating in the toilet for each person present. We took advantage of this to the maximum, so eventually they took out the stall walls and there was just open toilets in there. Fuck you, Mr. Patton! You are probably dead, but fuck you anyway!
Another thing we would do is gather around the payphone outside the side door of the school, and smoke. One of us would pretend to be on the phone, and the rest of us would gather around with our backs facing outwards to block the view. We would all huddle in a crowd and smoke marlboros. Don't ask me why we did it that way, it sounds retarded now that I type it out.
And lastly, the only time the police ever even came to my school was when some dumbass jocks were caught selling major amounts of steroids in the school parking lot. If we did get caught, we would get suspended two days for smoking, and three days for fighting, a week for drugs (I think, can't remember). You had to basically attack a teacher or commit a major felony to be expelled. These days, at least in my town, kids get arrested and expelled for both fighting and smoking.