You dont think the hanhallah and rabbieim forbid smoking in every yeshiva? I dont know of any yeshiva where it’s not weekly reenforced.
The buchrim want to fit in, so they follow their “cool” friends. Hanhallah does more than you can imagine to crack down.
That being said, when I was in yeshiva, the guys who had good self esteem and didnt feel the need to “look cool” as well as those parents that instilled the negativity of smoking/drinking/drugs- where the ones who’s kids stayed away.
Drill in the disgustingness of smoking and drinking from an early age. And keep emphasizing every time they see someone smoking how bad it is.
My parents CONSTANTLY did that w me, and I’ve never smoked or drank alcohol (other than kiddush wine) in my life.
I also never felt a need to feel cool with the cool buchrim because I always felt I was cooler than then by not smoking- and that stemmed from youth self esteem.
It’s not the parents faults. It’s not hanhallahs faults. Everyone is genuinely trying their best. I’m just saying for those who think their child cant be convinced- you’re wrong. Every bachur could be convinced if some properly.