What's going to happen if students go for exams with out studying & revising. They've got better chances to pass their exams if they're focused. Gambling's going to affect students focus it's a distraction which shouldn't be in their life.
If a student is distracted in class and neglects his responsibilities, he will not do well in exams even if he is not attracted to gambling. On the other hand, if someone is attracted to gambling but pays attention in class and uses their time properly, they will achieve good results even though they are attracted to gambling. Here, gambling will not destroy a student's career, but rather, if he is inattentive and does not use his time properly, he will destroy himself.