The firsts are easy to identify.

We write down things like a baby’s first word. We take pictures of the cake smashed in tiny fists at a first birthday. A first tooth, a first haircut, a first Christmas. These are not just remembered but often memorialized.

It is harder to recall lasts.

As our children grow, each new milestone comes with the end of an era. You don’t know the last bedtime story when you read it after years of “just one more.” Goading your child into taking a bath becomes a teenager who spends hours and all of your hot water in the shower without you noticing when it happened.

The first time saying “mama” makes you cry. You cry again when you realize you have just been “ugh, Moooom!” for months.

But there are some lasts that are easy to predict. They are the finish lines laid out years in advance.

When my son was born, I knew that, barring some kind of educational hiccup, he would be part of the Class of 2026. It wasn’t written in the stars. It was just math.

It seemed impossibly far away at the time — just like it is for every parent holding this frightfully small and completely dependent life. How can we imagine a time when this little thing that just eats and sleeps — or cries for weeks on end with colic — will someday stack up enough credits in American literature and biology and geometry to merit a diploma?

My life has become a series of reminders that my child is no longer a child. The fact he is taller than me is the biggest clue. The government believes he is an adult just because he is 18. If officials saw his bedroom, they might revise that position and classify him as some kind of raccoon. We are hip-deep in paperwork for college and financial aid. He has a job.

But we are approaching the tape stretched across that finish line, when he will graduate from high school. Each day, my email has a new message helpfully handing over information about tickets and timelines. They are meant as guideposts. They feel a little like ransom notes.

My son’s school career started in a preschool class at a YMCA. I walked him in to the room with two boys in superhero shirts and three girls named Paisley. His face lit up and he ran in, finding his people and immediately locating the plastic dinosaurs and lecturing about velociraptors. He didn’t cry. He just moved to the next thing. When he eventually looked up, he just waved and picked up a stegosaurus.

I have paid for his cap and gown. I have ordered a cake. People ask if he is excited to graduate. Not particularly.

He doesn’t recognize this as the ending that I do. Like that first day in preschool, this is where something new starts for him.

I can’t wait to see what he does next. But I’d be lying if I didn’t admit to missing the little boy with the dinosaurs.