Here’s how it works: We didn’t plan for this to happen but we’ve settled into a pattern where every Sunday, usually in the afternoon (after dinner in Pennsylvania), we FaceTime our son. My wife and I squash together on the couch, holding her iPhone at arm’s length, and peek into our only child’s new life.

It’s a little alien, partly because we actually resemble aliens in the little inset screen, but also because every time we FaceTime, I’m very conscious of how firmly the shoe is now on the other foot.

For the past 30 years, my parents have called every Sunday at 10 a.m. We talk for 15 to 30 minutes, depending on how much we have to say. Sometimes I’m not home, so they leave a message. We still do this.

There was a time when they called me at my dorm room, looking for a glimpse into my life away. We get a better glimpse now because we can actually see our son sitting in front of his laptop, glancing around, shooing people away who’ve come looking for his roommate (Why are they looking for the roommate? Why not him?), but it’s essentially the same drill: How are classes, how is your roommate, are you eating, are you doing laundry, what’s up?

He came home for the first time about a month ago. Not for the High Holy Days — he goes to college in Pennsylvania, not New York. For something called fall break. He was home for four days, during which time he saw approximately 23 movies, ate two boxes of frozen pancakes and a pound of pretzel twists, burned through a tank of gas and occasionally was able to hang out with his parents. In other words, the four days were an exact replica of his senior year in high school.

One night I woke up in a cold sweat, just as I did almost every night when he was in high school. I lay there, listening to him in the next room, wondering, “Is he really watching YouTube videos and eating pretzels at 2 a.m.?” That the rest of this familiar scenario — “Doesn’t he realize he has school in six hours?” — didn’t apply was irrelevant. I spun into a maelstrom of worry, understanding too clearly that at 2 a.m. next Wednesday, six hours before his 8 a.m. chemistry class, he’ll be watching YouTube videos. And eating pretzels. Nothing had changed.

Break ended and we loaded him onto a Newark-bound plane, me thinking, “Boy, it was great to see him, but I was hoping he’d be a little different. More grown up.” Commence another month of worrying whether he has the “life skills” to survive his freshman year. Just because you can’t hear the pretzels doesn’t mean they’re not being eaten.

Last Sunday we were on FaceTime, but this time he seemed different. Maybe tired, maybe burned out after a day of studying, maybe partied out (it was Sunday, after all), but in general, calmer. Older. He told us about his new radio show on WJRH, the campus station, and how he’d made it through a mob of applicants to lead campus tours in the spring. His calculus grade wasn’t where it should be, so he’d met with his professor and sketched out a plan.

We hung up and my wife and I agreed: “Man, he seemed pretty mature tonight, didn’t he?” Not at all like he’d be following up our conversation by settling into some early morning YouTube videos and pretzels. I’d been wrong. He had changed.

Which was what I wanted, right? Sure, and I hope he could somehow sense the pride that welled up in me later that week as I walked through the Financial District, headphones clamped firmly on my ears, listening to him play his DJ mix on WJRH.

But that’s not what I was feeling right then. Right then, after we hung up, I turned to my wife and put into words what had been nagging at me with equal parts melancholy and wonderment during the entire call. Just a little reminder that with growth comes new challenges.

“Boy,” I said, “he really doesn’t live here anymore, does he?”