Decades ago, I shifted from minimum word count (which matches grading/ranking student writing as one of the more counterproductive pedagogical strategies) to maximum word count--e.g., "no more than c. 1200 words." The logic is obvious--as is the dis-logic of minimum word counts.
About two years ago, I started using time: "see what you can do in about one and a half hours of writing before posting. Spend about an hour writing and leave yourself at least a half-hour to look it over and make any changes."
I'll just say this works: when the students know that their primary audience is other students in the class (remember, I don't grade), they are concerned with how they textually appear to their peers--let's just say they care more about them than us. When you ask your students to spend about an hour and a half writing, about half of them will spend three. Students are not dumb. They know that what they write and how they write shapes how their peers will see them. We don't need grades to teach them how to see this.
I have been thinking about revision. I have for decades used the first draft/second draft/final revision. We have long noted that when students are writing with computers (like us), revision is not a matter of drafts. Now I hardly ever ask students to revise. I know they are revising as they write and before they publish. Today, I wrote a post on the CWPA list about the link between authentic revision and reading aloud to peers.
I have realized that there's a-textual revision. As well as revise before they send, students virtually revise when they read what others have written. Revision is in their minds: they see what others have done, particularly those who are getting serious responses from others in the class, and they think, maybe I could have done this or that, included or excluded, been more personal, taken a few risks, heard myself speak through writing. When students do this virtually (and I get them to write about it by inventorying their experiences about writing, reading, and being read), they are learning about writing. They don't need to rewrite. Sometimes, they just need to write something new, remembering what they learned from what they last wrote.
I can't help but add: I have been reading somewhat impatiently on the list about all the time teachers waste by having their students read out of readers--as if students don't have a million things to write about intimately connected with their lived experiences. Publishers and academics make money out of these readers. Teachers have students kill time by reading and writing/discussing about what they read (this is the critical-reading strand of our field). Ways of Reading was one of the worst exercises in this misdirection of writing instruction. If you really want students to learn about writing, have them write--all the time, writing out and writing back and forth to each other. I am hardly the first to note that we learn to swim by swimming, not by reading about how others swim.