in high school, my friends and i frequently snorted ritalin/adderall before going to class. once i drank a bottle of sprite and raspberry vodka in math (9 am on a tuesday...verrry cool). it was a class of twelve kids, and i was sitting like one or two seats from the teacher...didn't get caught, though. i don't think anyone suspected the stimulants at all....the school was very demanding, and i think the teachers were used ot seeing kids in various cracked out states from sleep deprivation, too much caffeine, etc, so we probably didn't stand out on stims.
in college, i have been to class on weed, opiates, benzos, stims, and drunk (of course...although only a few times.) weed, alcohol, and benzos don't really improve my intellectual experience, but i have found that going to class on opiates is enjoyable and makes the material more interesting. stims...well i don't really enjoy them much, but they do make me hyperfocus. never been close to being caught...then again, i think it's pretty difficult to be caught in college.