Poor grammar does not make my argument nil nor does it make your argument valid.
I'm really not sure what argument you are trying to have with me or why. If you're saying that I can't prove that students today couldn't pass a general final exam from 1900, you are correct; I can't prove that. It is an opinion I have formed through years of teaching.
I will maintain that opinion until other evidence comes to light.
It seems as though you are trying to provoke an argument with someone who expressed an opinion by saying "Prove it!"
Finally, poor grammar does not make an argument true or false, as you so aptly stated, but it doesn't help your cause either. If someone doesn't understand what you are saying due to poor communication on your part, please don't rail against them for pointing out an incoherent sentence. I really don't know what "Being taught them and being able to learn them... means. Again, I'm sorry if my inability to understanding what you are saying has offended you. Maybe if I used my own critical thinking skills I would be able to determine what you meant.