My eldest is at primary 3 now
and so I know how or what a primary 3 kid is capable
you really think a primary 3 kid has the strength and courage
to take a knife and even dissect a live chicken??
		
		
	 
he dun have to dissect. he just have to poke another kid with the knife. depending on where he poke (which doesn't require much strength)  he could make the other kid handicap for life.
poke at the throat...potential to kill
poke at any part of the face...scarred for life
poke at the eyes...permanent blindness
doesn't have to be a knife...can be any sharp object within his reach...pen, scissors, penknife...these may be easily found in their stationary set during arts and craft lesson.
children these days are very desensitised to violence from the media and games they are exposed to at a young age. They don't think of the severe consequence hurting someone in real life have because to them, its like a game or something they see on their small screens or tv. life has no reset button. 
its up to the adults to correct them at this age.
you may know what your primary 3 kid is capable of....but you don't know all the pri 3 kids out there in the world and their background and upbringing.