Think outside the box. Plant cocaine in his big brother's locker, than leave a tip to somebody who works in the school. It doesn't have to be cocaine, but if it's too light a drug then it might not work. Other contraband in schools are also an option. If it's hefty enough you can get him flat out expelled; he probably had it coming. With him out of the way, next time the whiny lil 12 year old wants to pick a fight with you, pick him up off his feet and charge into some lockers or a wall. Although without his brother there he might just leave you alone, unless he knows you planted the evidence.
Just make sure your school rep isn't harmed by this.
Just make sure your school rep isn't harmed by this.