Help.

Anyone with experience is invited to offer suggestions on cost-effective activities to keep 11-12 year old boys occupied, so that they don't get bored and start throwing hard things at each other "for fun" and corrupting the younger children for back-up and amusement.

I mean, seriously, apart from computer games and television, is there Anything that will engage, for any reasonable amount of time, a rather edgy group of cynical preteen deviants?