I used this idea and now 2 out of 3 friends are leaving my life for good!
Simply dont show any attention to them, say hello and bye. but dont invite them out on the weekends, dont call them nothing. and if they ask you, then come up with a excuse.
If you have a party, dont invite them, let them hear your having one come over to you and act surprised to hear you 'forgot' to invte them.
You can still say hi and talk to them! You don't want to be rude! if your having a party and you don't invite them, then don't let them find out! you don't have to invite them over or go anywhere with them if you don't want to but at least be nice! if they go to school with you then just keep them school friends! Goodluck!