When you come across an example of student writing that is particularly well-written, you can share it with other students. However, avoid using negative examples, as most students will hesitate to give permission if they know you plan to use student writing to exemplify poor writing–and not telling them of your intent would be unfair. Furthermore, students will learn as much from positive as from negative analysis. No piece of writing, your own included, is so perfect that constructive criticism cannot be aimed at it. It’s best to ask all students to sign a release form at the beginning of the semester granting permission to use their work for teaching purposes. Note that if you wish to quote their work in an article on teaching, you’ll need specific permission.