I know schools prohibit cell phones but they can be very helpful and with prepaid phones also fairly reasonable.

Can't believe I'm actually suggesting this. However with busy working parents and kids involved in extra after school activities it's a great way to keep in touch.

And 911 is just a cell phone away.

I actually used my cell about a month ago to report an accident. I was stuck in traffic and going the opposite direction so couldn't stop and help. But I could dial 911.