im stil enraged about hearing about all this and i swear i felt like punching the cubical wall down wheni read certain parts.
anyways...in high school, i used to run with the wrong crowd, and i left, and although i did not get beat upon, what she ways is true. The crowded that you leave almost instantly hates you. Its even worse when the females get involved. We had a student lifelined (helicoptered) to a local hospitol because SHE got jumped by numerous, numerous kids/teens. 
My point is it doesnt surprise me. it might sound ubsurd but this stuff does happen. i wouldnt deny the childs story for one second and give you my full support. the problem is these kids that did this dont care about pretty much anything. and the girl who called them needs to be smacked and i hope she gets punished by court just as bad as the boys. 6 on 1 is a cowards game. 
if it is a pick on the handicap game, then that is the motive. but with a girl involved, something doesnt add up. was he seeing this girl? and maybe one of the 6 was a bf of some sort, and well, tehn its revenge.
Just brainstorming, also, you said 5 where issued warrants...dont let the 6th get away. i may only be 19 but i saw this kind of stuff everyday for 4 years in High School. dont let them get away.