Some teachers think that basing 20-30% of the grade on grammatical and stylistic matters is unfair unless they mark all the flaws. We approach this issue from the perspective of readers. If you review a textbook and find editing mistakes, you don't label each one and send the text back to the publisher. No, you just stop reading and don't adopt the textbook. Readers who are not teachers just don't keep reading is a text that is too confusing or if errors are too distracting. Readers who are teachers are perfectly justified in simply noting with an X in the margin where a sentence gets too confusing or where mistaken punctuation leads the reader astray. Students are resourceful (they can get help from our on-campus Writing Center office or our Writing Center website) and will figure out the problem once a reader points out where the text stumbles. That's really all it takes.