This argument is similar to one often given for not voting - "my vote won't make any difference". True, one person declining to dissect a frog in class makes little difference. But if every vegan and vegetarian declines, that makes a HUGE difference. (Best case scenario: schools start asking BEFORE obtaining the frogs, which makes students aware that they CAN refuse without risking punishment, and the number of animals dissected in the country drops significantly). And there doesn't need to be any organisation if everyone simply acts based on their morals and feelings, rather than resorting to the "it's dead anyway" / "my vote makes no difference" argument.
this is where your argument falls short. not everyone has the same morals and values. not everyone gives a shit about the tiny frog. my entire science class dissected the frog (7th grade) and in my sophomore year, everyone but 1 dissected the pig (the smell got to her). and in my anatomy class everyone dissected the cat. obviously the margin of error here is pretty large, but my point is that a lot of people simply don't care. if science and the evolution of our species is at risk because of a moral, we'd get nowhere (I suppose if you need an example you could look at The Dark Ages which loosely fits what I'm saying). you do realize a lot of medicine was tested on animals first, right? I'm not saying there is much to be gained out of dissecting a frog, but it's the principle of the matter.
evidence? what evidence do you need? go hold a knife up to one of your pets and it'll stand there like, "what the fuck are you doing?" it hasn't learned knives are dangerous. as a baby you didn't know knives were dangerous either. you learned from other people or maybe even personal experience. so unless there's a pet mothership beaming down information to your animals, it has no clue what a knife is and how dangerous they can be.
if a cow was treated right on the way to the slaughterhouse (remember, I am against animal brutality because I know animals are sentient) and treated it properly before it died, how will it know it was being sent a place of animal murder? treat it humanely before it dies and give it a humane death (a painless syringe with painless chemicals that kill it almost, if not instantaneously) how is it going to know you were killing it? it might think it's on its way to the best spa treatment in Bovineland.
you need no study when you can prove it yourself. hands on experience just like dissecting frogs, eh?