Pointless Digression and every other one of you reading this who works with kids today,
Stay strong. Stay strong for them and support them and love them. They need us right now, even the cynical teenagers. All weekend long they've likely been bombarded by media in one form or another, the social network sites they are on are bursting at the seams and some of them are scared and angry and worried and anything else you can name. You are one of the safe, calm, trusted adults in their life who has their best welfare in mind and they know it. They need you today. Make it for them.
Then when that bell rings and you send them off, make it for you. It's okay to let go when they're gone. Use the catharsis of tears or anger or numbness to help you cope so you can be there again tomorrow for them. I know that as soon as they are gone and I check on my fellow teachers, I plan to shut my door and put my head down and just let it all go.
Don't live in fear. Be smart, be safe, but don't let this run your life or your classroom.
Love the students, lead the students, teach them by example today as much by your lesson plan.
Hug them if allowed, and hug your fellow teachers and administration and staff.