BEST WISHES: Children at a kindergarten in Weifang, east China's Shandong Province, send New-Year gifts to their foreign teacher on January 10, 2009 (XINHUA)

From 2005 to 2012, I taught English in China. I enjoyed the focus Chinese society placed on education and the respect students had for their teachers. My students used to tell me, "If you're my teacher for a day, you're my teacher for life"—a sentiment based on an old Chinese saying "yi ri wei shi, zhong shen wei fu" or "My teacher for a day, my father for life." I didn't know how true this was until the tragedy of the Boston Marathon Bombing last year.

My students were bright, eager learners, so it was inevitable that some would look to the United States to further their education. The first of my students to go there arrived at the University of Alabama in January 2007. She e-mailed me often during her first weeks, telling me of her difficult adjustment: the lack of public transportation, differences in food, how fast people spoke. The culture shock was to be expected; I counseled patience and told her she would eventually adapt.

But I knew one side of U.S. culture would never be something one just "adapted to." Random violence, especially involving guns, was something Americans lived with more than Chinese. One such incident came just months after my student had arrived, with the Virginia Tech massacre in April 2007 (32 people killed, 17 wounded). I wondered what my student's parents thought, with their daughter not only in a strange, far-off country, but in an environment where such shootings happened with alarming frequency.

Before long, my student got the hang of things and our e-mails became sporadic. I checked in once in a while—Spring Festivals and summer vacations—and was happy that she was adapting well. Then a couple of years later, I awoke to the news of a shooting at the University of Alabama (3 dead, 3 wounded). I immediately thought of my student and how I could contact her to see if she was safe. When I e-mailed her, I was relieved to learn that she had just begun a Ph.D. program in Ireland that very month.

Other students left for the United States in the next few years. Fear of violence crept into the back of my mind, but thankfully there were no incidents near them during their stays. Then, in my last semester before I returned home in 2012, one of my students asked for advice about applying to a summer work program in Denver, Colorado. I'd only known her for a couple of months; in fact, I'd hardly noticed her until the day she stayed late to ask me questions. Still, in the tradition of the old Chinese saying, I thought, "My student for a day, my student for life." I helped her as much as I could until, a few weeks before the end of the term in June, she set off for America.

I moved home early the next month, after seven and a half years in China. Less than two weeks later, James Eagan Holmes opened fire in a movie theater in Aurora, Colorado, a suburb of Denver (12 killed, 70 wounded). Again: Was my student safe? I e-mailed her as soon as I heard the news. I had no idea where she lived in Denver—or whether, in fact, she lived in a nearby suburb such as Aurora. I don't actually live in Boston, for example, but I often tell people that I do because it's recognizable; she may have done the same. The shooting took place at a midnight showing of a Batman film on its release date, just the sort of cultural experience that a young person might want to take part in. I waited three days with no news.

On July 24, I got a reply. I was right that my student wasn't in Denver itself; however, she lived west of the city. She told me not to worry before continuing, "I feel sad for Denver. I still think America is a good country and l love this state where l stay now. Every country has crazy guys, the United States is not an exception." I was again relieved—for the moment. Another student, another bullet dodged. Literally.

Afterward, none of my other students went to the United States that I was aware of, and I began my new life back home. Then came the Boston Marathon Bombing last April (3 killed, over 250 wounded). Among the spectators who died was a Boston University graduate student: Lu Lingzi, a 23-year-old woman from Liaoning.

Lu's fate was my worst nightmare come true, and I mourned her as if she were one of my own students. Though I didn't know her, Lu embodied those students I did know—and others like them who seek their way in the world. They come and go like youth everywhere, fearless and unaware of potential dangers.

Then came the e-mails­—from Zhejiang, Sichuan, Hainan. My students in China, knowing that I lived "in Boston," as I'd told them, contacted me to see if I was all right. One student I hadn't taught in four years showed her good memory along with her concern, writing, "I know that you don't like crowds, you may not be there. But since Boston is your hometown, I'd like to make sure that you're all right. Sorry about the tragedy."

"My teacher for a day, my teacher for life." Old sayings are just that. But when they are put into action, they become truths.

The author is an American who worked in China