When I was in school (back in the olden days) grammar and sentence structure was part of your English class. Neither of my daughters (23 & 21) were ever taught how to diagram a sentence in elementary or middle school. While in high school my older daughter took advanced Spanish classes and said she learned more about sentence structure in those classes than in any English class she ever had.
According to one of my teacher friends, it was taken out of the curriculum (just as penmanship was) because it was no longer deemed necessary. The focus has become the material included in the stanardized tests students are now required to pass.

