Maybe they're really just F#(&ing stupid and there is no hope for them. I agree that a lot of the problems with our youth these days is the result of bad home structure. So if some kid starts mouthing off at me for something stupid (depending on my mood that day) he just might get the A55 whoopin' his daddy should have given him.
I know while we raised our son I had to always remind him not to write like we speak because the tone can't be conveyed in writing as well as in language. Of course, he gave me that look like,"what do you mean? It sounds good to me".
I then explained to him about how even penmanship could make the difference in him being overlooked for something he may want in life (possibly a job or something else very important) because no one will take someone serious if it looks like a second grader wrote those words. It took him a while but he no sooner than later started to see the light and now takes pride in his efforts in this regard. He's still not the best speller, always has been his weak point, but he has improved dramatically and grammatically and gives it his best. The main thing is he tries.