My sympathies to you and your students and fellow teachers. My counseling
experience has taught me that giving students opportunities to express
grief is the best RX. Cards, student created memorials are wonderful
avenues for venting their feelings and to overcome feelings of loss and
helplessness. There are great resources out there for grief. Kubler Ross
(Death and Dying) is one author who comes to mind who can help explain the
stages of grief: anger, frustration, acceptance, etc. The students to
watch are the loners; close friends who need more time venting in a safe
environment with small groups; ask a competent parent to help, if
counselors are in short supply.
Prayer is the greatest source of healing, of course.