The American Foundation for Suicide Prevention has programs to educate both teachers, students, and parents about depression. They also offer free downloadable packets; one that particularly caught my eye was one which included letters which the district can use in the case that a student does commit suicide.
Knowing what depression looks like in a student's behavior as well as how to help those students is imperative. The Association for Supervision and Curriculum Development (ASCD) provides examples of how the symptoms of depression may look like in the classroom as well as strategies the teacher and student can take to prevent it from getting worse.
The NIMH has put together a useful handout which they encourage you to print out and give to your students which details what depression is and any questions they may have about it. This can inform your students if they recognize the symptoms and encourage them to seek help!
What exactly is depression? The National Institute of Mental Health (NIMH) has a description of what depression looks like in teens. While the exact symptoms vary upon the particular student, depression is a period of sadness and apathy towards life.