Expressive writing requires no skill other than the ability to write words on a page. All that matters is that you express your feelings as accurately as possible into your writing. This writing is for no one to see besides yourself, so you don't need to stress about making it perfect. Unless you want to share it. This is your writing to do with it whatever you want. 

From my own experience, absolutely, but you don't have to take it from me. A journal from The National Center for Biotechnology Information covers an experiment done by James W. Pennebakerin which he concluded, "It allows reflection upon stressful events and the elaboration of associated feelings that, in the long run, may overwhelm the person’s ability to cope with emotional detachment from experience." -The National Center for Biotechnology Information

It can be, but, in regards to the prompts and activities shared on this site, I am writing them for the sake of relieving stress and boosting confidence, not to treat any sort of mental illness or trauma. If you would like more information about the subject, talk to a licensed therapist about more potential benefits of expressive writing. 

Teens are stressed. Many teens don't know how to manage their stress, and teens are the most vulnerable to other, more dangerous ways to elevate their tension. In an experiment done by Harris Interactive Inc., it was discovered that "Many teens also report feeling overwhelmed (31 percent) and depressed or sad (30 percent) as a result of stress. More than one-third of teens report fatigue or feeling tired (36 percent) and nearly one-quarter of teens (23 percent) report skipping a meal due to stress." -American Psychological Association. Introducing creative writing to students is not only a great way to improve writing and creative skills, but it also offers a great outlet for teens who need it.