http://abcnews.go.com/Health/AllergiesFood/year-virginia-girl-dies-allergic-reaction-school/story?id=15295949#.TwYZpNXp66A
My nut-allergic son is required to have one. Thankfully, the school nurse is on top of it; they called within one week of its expiration date last month (it still would have been effective, but better to keep it up to date). Alternately, teachers and other parents are not as educated or responsible though. Unfortunately, I have little choice but to trust my 5-yr-old's judgement-- and continually remind the teacher, especially on party and holiday days.