One student needs to be told--repeatedly, on every paper--that dashes are like Tabasco sauce: a little bit goes a long way. Another asks--out loud, in front of everyone--"What's a dash?" (And she's not kidding.)
And then there are the punctuation avoiders, students who pile word on word and phrase on phrase without a shadow of a hint of a comma and who approach the semicolon as if it were about to bite them and who have to be reminded that a question should end in a question mark and who even sometimes forget to put an end stop at the end of the sentence as if it could go on eternally and infinitely and neverendingly and lots of other synonyms students like to find in the handy thesaurus they keep always open on the laptop screen to allow easy access to words that are often right but frequently only almost right and sometimes dead wrong and when will this sentence ever end and what was I talking about anyway?!
Ah yes: punctuation! It's a beautiful thing. I'm not going to mourn its imminent demise as long as I see commas deployed elegantly in the occasional paper, but it's really difficult to teach proper use of the dash to students who've never seen one--and don't even get me started on the colon. Once (this is true) I detected a case of plagiarism after a student used a colon correctly, such a rare occurrence that it put me on my guard. When I encourage a student to use a semicolon to connect complete sentences, half of the time I get either a colon connecting sentences or a semicolon connecting dependent clauses. (And if you know why that's funny, you are a certified grammar nerd.)
Hyphens (not dashes!) do one kind of job,
virgules (or slashes) another.
Ellipses replace the deleted words.
(Students ask--to my face--"Why bother?")