Actually the teaching of grammar has no demonstrated effect on grammar in a student’s writing. Native speakers have far more grammar in their heads than linguistics can describe. Usually people mean punctuation when they protest grammar, but when they actually mean syntax, the problem usually isn’t student ignorance. Rather when students learn to write new forms with new vocabulary and complex syntax, the strain of all the newness causes error. Most just haven’t proofread adequately.
As digital man goes faster and faster, most of us are proof reading less. We are unlikely to return soon to the leisure of elegant prose.