How's it the school's fault?
Never come across a school that permitted drug taking on school premises, or condoned the use of drugs out of school either?
Most schools devote more time than they should (cos it diverts from the 3R's) trying to teach children that drugs are BAAAAD, very BAAAAD & they should "just say no" for reasons of health and legality. Schools teach this despite all the bombardment from wider society that drugs are cool, the route to quick riches for the poor etc, etc. Some schools teach drug awareness despite the best efforts of the drug-using parents of the pupils concerned. WTF else do you want schools to do?
Kid done wrong, kid was caught, kid kicked out! Kid will be subject to due criminal process as a result of the schools actions.
(So an example hereby set for any other little monsters that might be tempted to subvert a cookery lesson from the defined parameters of the national curriculum in future).
Teenagers are by definition feral little monsters and it takes the combined efforts of parents, teachers and the wider community to keep them in line till they surface from the adolescent hormonal fug as rational adults.
I have an awful lot of complaints with the current education system, & a lot of issues with current drug legislation - but I can't for the life of me see how this incident is the fault of anyone but the young person who chose to commit a criminal act on school premises. (By 14 school will have taught him that his actions were criminal).