I’ve certainly had those moments. Those moments when a student has written something or said something or done something that set off alarm bells.

My first was two days into my first year of teaching, when one of the freshman boys in my advisory class brought half a dozen bullets into my classroom and proceeded to play show-and-tell. The same student, I learned, had a history of making threats to teachers and also, unsurprisingly, a mental health history. As a Special Ed teacher, I’ve had several students who fit the same profile: a history of emotional and behavioral disorder, occasional threatening statements, acting out, made all the more troubling by an unwillingness or inability to effectively communicate their frustrations or desires. With these students, I remember the advice of an early teaching mentor: “Do what you can. Do what you must. Hope for the best.”

And I try. I was trying on our last day before Winter Break, December 14, when Sandy Hook happened. The principal came over the loudspeaker. The classroom TVs popped out. The class Christmas parties and final assignments were stopped midway. Collectively, the entire staff of our school–every single teacher–just couldn’t do it, just couldn’t get up at the front of the classroom and go about business as usual. We all knew it could happen here. Only difference with me is that I specifically knew, if it happened here, who would have the greatest likelihood of making it happen. I knew the names. I knew the faces. I knew the psych reports.

The questions I continue to ask myself are: What does this knowledge mean and what does it entail? If I know that a particular student has had a severe mental illness, if I know that he’s made threats or had violent outbursts, if I know his background has elements in it that parallel elements from the backgrounds of young men who’ve ended up taking the worst action possible, how do I “do what I can” for him? And, perhaps more important, how can I “do what I must” for everyone else?

I want the answers to be concrete and simple. I want them to be applicable to all situations and to all students. I want them to be infallibly right.

In truth, though, I think they can’t be. Anyone who has taught or dealt with or had children knows that they are complicated and uneven–that what they say they don’t always mean, and what they think is not exactly what they end up doing. If who they are in the morning is entirely different from who they are in the afternoon, how much greater is the distance between who they are in September and who they are in June, or who they are at 15 and who they are at 18? Possibility. Peril. You never know precisely which until later.

In my own experience, this goes doubly so for children with mental illness. You never know, upon first encountering a child whom the school district has categorized as “emotional disturbance” (ED) or “emotional and behavioral disorder” (EBD), what the real dynamics are and what they will be at the end of the year. You never know precisely what effect a change in medication or in dosage might have. You never what a change in foster parents might influence. Whether a child ends up institutionalized. Whether he ends up in student leadership and AP classes and gets a 3.7 GPA. I can match both fates to real faces.

If there’s one thing I have learned from experiences like these, one white spot amid the shades of gray, it’s that you can never close the book on a child, and you can never–most important–eye him with suspicion or treat him as a potential enemy. The trust that underlies the relationship between teacher and student, like that that defines the relationship between parent and child, is delicate and volatile. Children, whether they’re seven or 17, can be lifted up or brought down by what you might see as the most insignificant and fleeting influences, and they notice and imitate the behaviors they see from the adults around them. Children who see their parents and teachers caring for others and acting empathically generally end up caring for others and acting empathically. Children who grow up in environments marked by violence and suspicion and intolerance generally end up violent and suspicious and intolerant. They become what they see, and we are always in their line of sight.

For myself, for my students, I hope that what they see will help them become great or good or both, whether they stay in my classroom or go off to non-public, specialized schools, whether they meet only success or find life difficult and disappointing. Whatever the future, I do know that, in the present, the best I can do is to show what care, compassion, and effort look like.

Needless to say, to my mind, the best instruments to use to accomplish this continue to be the book and pen and not the rifle and the bullet.