Does anyone know specifically who the yoots were that attacked the school?
Yes - they were all later arrested and faced the courts, and the two oldest (both over 18) got three years each, while the 17 year old boy who actually used the meat cleaver got nine years. Five younger boys (about 13 and 14 year olds) escaped custody and were put into various programs.
It was a random gang attack by a group of thugs on boys at a private school. The one who was jailed claimed at his trial that it was a revenge attack because one of the private school boys had supposedly raped the sister of one of the attackers but no evidence of this was presented beyond his claims.