Traditionally, writing is part of most language arts classes. We teach students grammar and composition, expecting them to carry that knowledge into other classes and into life. Most teachers include in their grading rubrics sections on organization, coherence, and technical (grammar) skills. Some teachers, especially in middle school and junior high, also seem to reteach their students how to write while developing the paper.
That’s how important writing is. It’s a means of communication that you have to be proficient at, no matter what field you go into. Many teachers realize this and try to prepare their students the best they can. An unfortunate number of students regard it as torture (because anything requiring actual work is torture when you’re a teeanager), develop a hatred for it, and refuse to write their school papers.
Instead, they whip out their phones and type up a poorly worded, poorly spelled, poorly structured complaint, which then masquerades as a Facebook status.
I haven’t found a way around this cycle myself, except to explain to my students that every single text they send is writing, and grammar is what’s allowing them to both speak their mind and understand what their friends are trying to say. It doesn’t work, but they slowly start getting that they’ll never get away from writing.