On occassion I have smoked in class, only when I thought I had a good chance of getting away with it though. Also in an alcove behind my school and in the lower hallway once I knelled at my locker for cover to sneak a few hits...no one was around so I figured I could catch a buzz and get the fuck out of that hallway. Never been caught, only one close call where I hadn't actually sparked up yet but the teacher suspected I did and threatened to tell my administrator.
Here in America according to the ACLU a group of students cannot be searched just because one is suspected of having marijuana. So even if a teacher/admin could smell smoke comming from an area near you and five other students you should not be searched. If you're caught holding a bowl with smoke in your lungs...thats a different story.
Second to that I consider smoking at my house with family home pretty fuckin risky.