Still hard for me to believe that number but I can certainly see any degree of general acceptance and use having bad effects on achievement. They weren’t allowed to use it out in the open during school hours were they?
It wasn't a question of whether they were allowed, it was if they thought they could get away with it. The introduction of edibles and vaping THC reduced the detection probability of smoking pot.
My number included experimenters, occasional use and hard core users. I'd say about 35% are totally addicted to the stuff and use it every chance they get. An easy 50% more are opportunists. They use it if offered. The other 10% are socially pressured to use it when in groups.
There were a few holdouts and they were mostly Mormon kids.