Some of the comments are astounding. If a kid armed with a knife makes every effort to avoid a confrontation with a bigger kid, including getting off before his scheduled stop, and gets followed, taunted, and punched in the back of the head, when exactly is he finally allowed to defend himself? In terms of the number of stab wounds, I'm guessing he kept going until the older kid fell. For those who say 12 stabs were overkill, I think only two of them were showstoppers, so had he only stabbed him six times, the other kid quite possibly could have turned the tables on him.