I (think I) see where the distinction is, though it's certainly arguable. If I picked up a gun and aimed at someone's leg and not with the intent to kill them, pulled the trigger but I was a bad shot and got them in the head instead, would that be manslaughter or murder? I'm guessing it would be murder. I've got to think that not only intent but the context of what is likely to happen should be considered.
I do believe hitting someone in the head with a heavy plank of wood -though perhaps not with the intent to kill them -should be classified as murder as I have to believe the assailant would realize that it is not out of this world they could kill someone with this deliberate and planned action.
Regardless, a sad situation. Certainly saddest from the victim and family point of view (bet they'd want him to be charged and successfully prosecuted with murder I'll bet), and sad from the point of view that this kid even did this action in the first place and is probably going to be out in society again. I wonder what the possibility will be of him having true remorse and a conviction to change his life hence forth?