They walked down the road from the lake about 100 yards ahead of us, bouncing off one another shoulder-to-shoulder about every three steps, in animated conversation. Nothing new—Katie and Nathan are almost always in conversation. I feel sure they were talking about nothing particularly deep or important at the moment, but they were continuing the step-by-step farewell that occupies our family right now as our daughter prepares to leave for college.

We are parents of five, with births spread across 16 years and four presidents. But for the last eight years, we have been parents of two, the classic one-girl/one-boy family of four. Easily seated in cars and at the dinner table, evenly matched in our ability to tease one another, we have had a delicately balanced ecosystem that has served us well. We have grown together as our last two kids have grown up, and we have a drawer full of common experiences that are not shared by our older kids. We are the Shaubs, Updated Edition.

But all that is about to change, and I find myself wrestling inside with what it means for my life. I have three more years to invest in Nathan, and I am excited about the things still ahead of us. But the sun is setting on our parenting days the way it does at the beach, when you watch that orb disappear like liquid into the water in a matter of seconds. I wonder what comes next.

The little lake house is one thing that comes next, a place to write, to play golf with Nathan, to read, to spend time alone with my wife. It is a place to walk and to bring grandkids, or at least we hope it is. It is a place of the later years. If God grants good success and economic stability, it is a second home; if not, a first.

My investment in students, and my search for wisdom, continues. I have a group of friends with whom I can be honest, and I have the woman I love close by me. I hope for 15 productive years as a professor, perhaps 20.

But Katie is leaving. Leaving. Parents understand what that word means, and it does not mean what it means for the kids: freedom. For parents, a child leaving brings a mixture of pride and loneliness. It leaves a sense of accomplishment and despair simultaneously. There is absolutely nothing else I can do to get her ready for this. And there is absolutely nothing else I need to do.

I have done this three times before, so I thought I would be practiced and poised. In my job I watch parents go through it year after year with bemused detachment. But it is my turn again. And it is my Katie who is walking out the door.

We will regain our equilibrium. The gyroscope is spinning a bit out of control, but we will calibrate again. There will be a new norm, with one side of the dinner table empty. And with my son as a new driver I will sometimes be in the back seat.

In fact, that’s how it feels. It feels like, after all these years of being the Dad in the driver’s seat for all those family trips, I am being relegated to the back seat. You can’t see as clearly back here, and other people seem to be making the decisions about where we are going.

For many years, particularly with Katie and Nathan, we sang at the beginning of each trip out of town, “We’re going on an adventure, and we don’t know where.” Today, for me, we are. But with one seat empty.

It was a seat that held giggles and baby dolls. I will look in the back seat and see Amish romance novels and adventure stories, a cheerleading outfit and a megaphone. I will see an iPod with one ear bud in Katie’s ear and the other in Nathan’s.

And then, I’ll turn around, face forward, look out the windshield and drive on. We raised her to leave that seat empty some day. And when some day comes, driving on is all there is to do.