One of the most common responses to the question, "Why did you give me a paper so full of mistakes?" is this: "You're the teacher; you HAVE to read the paper." Sadly, students often see teachers as a captive audience who will just put up with whatever text flows from the keyboard or pen.
Most students can edit their papers, and they often believe that editing doesn't matter so they don't take the time to do it. Or they wait too long to finish a paper and don't have time to edit. Sometimes the biggest part of the problem is getting students' attention focused on editing. Teachers who don't want to be distracted by proofreading errors or relatively simple editorial glitches report that the number of errors diminishes quickly when 10-20% of a final grade is based on editing.
But if you don't like carrying such a big stick, then a couple of other strategies might help you get cleaner papers with few editing and proofreading problems: