Remember that old Robert Fulghum essay and best-selling book, “All I Ever Needed to Know I Learned in Kindergarten?” An ode to the essential lessons of life, it contained nuggets of wisdom most of us picked up in the sandbox (along with the occasional case of pinworms):

“Share everything. Play fair. Don’t hit people. Put things back where you found them. Clean up your own mess. Don’t take things that aren’t yours. Say you’re sorry when you hurt somebody. Wash your hands before you eat. Flush …”

I experienced a refresher course, of sorts, at my elementary school reunion last weekend. And while I doubt these essential lessons are best-selling book fodder, I present them to you in an essay titled “All I Ever Need to Remember, I Learned at My 40-Year Grade School Reunion.”

No matter how calm and relaxed you think you are, frantically fluttering butterflies will commandeer your stomach the minute you walk into your old cafeteria filled with 38 classmates you haven’t seen in decades.

The butterflies cease and desist as soon as you look around and realize everyone is just as panicked as you are. (And a stiff gin and Fresca doesn’t hurt, either.)

A lunchroom that seemed cavernous and intimidating at the age of 9 looks so much smaller to a 53-year-old, you’d swear they cut it in half. And who shrunk the lunch tables, anyway?

Nametags should be mandatory at reunions of 15 years or more. (In our case, the organizer thought it would be fun if people didn’t wear nametags for the first hour, as a kind of icebreaker. A good idea, in theory. In practice? Absolute torture.)

If a person reasonably maintains his or her weight, retains most of their hair and sports no facial hair (his OR hers), they tend to look very much the same as they did in eighth grade.

The theory above exempts about 70 percent of people over 50.

Balding men are the most difficult to recognize, followed by men with facial hair. Bald men with facial hair? Fuggettaboutit. Just ask him his name, try not to look dumbfounded and go with it. Look closely and you’ll see the same eyes and smile behind the whiskers.

In general, the years are kinder to women than they are to men. Sorry, guys, but it’s true. (And, yes, we have the multibillion dollar cosmetics and hair color industries to thank — or blame — for that.)

After two hours and three gin and Frescas, it becomes difficult, bordering on impossible, not to ask someone if they’ve had Botox or collagen injections. (Don’t worry. I held my tongue.)

It’s amazing how good it feels when someone says, “You haven’t changed a bit,” even though you know A) they’re lying through their teeth or B) they left their glasses at home.

Some of the most interesting and fun people are the kids who seemed to keep to the shadows in grade school. Late bloomers, it turns out, are pretty cool.

Forty years later, none of the old labels — popular, nerd, bully, stuck-up, gross, jock — still apply. Everyone is in the same 53-year-old boat, trying to stay afloat and enjoy the cruise.

The poor kid who was always getting beat down (and I mean that literally) by strict, yardstick-wielding nuns will, 40 years later, rise again as a hero, recounting those battles as if they were fought on Omaha Beach.

It’s a sure bet that one of the quietest, most demure girls in your fifth-grade class will be the one hogging the microphone and singing class songs at the top of her lungs. Witnessing this will make you incredibly happy.

Ask five people to recount an infamous incident from sixth grade, and you’ll end up with five vastly different versions of what happened. It’s now a mystery who, in fact, was thrown up against the blackboard by the hairs on the nape of his neck by Sister Michael Mary. But, whoever it was, he was apparently still too sore to attend the reunion.

Five and a half hours sure flies when you’re having fun.

Of course, to have a successful reunion, Fulghum’s advice still applies, “Share everything (including your gin). Play fair (wear nametags). Don’t hit people (and don’t invite Sr. Michael Mary). Don’t take things that aren’t yours (like another classmate’s spouse.) Say you’re sorry when you hurt (or interrupt) somebody. Wash your hands before you eat (the hors d’oeuvres.) Flush …”

— Cathy Hamilton is a 53-year-old empty nester, wife, mother and author, who blogs every day at BoomerGirl.com.