If you’ve ever chaperoned 16 middle-schoolers on a cross-country field trip, congratulations.

You’re a stronger person than most of us will ever be.

Even if you’ve never chaperoned 16 middle-schoolers across the country and around the nation’s capital and through all those museums and cherry blossoms and blisters and bathroom breaks, you still know the first rule of field trips: Where the kids go, you go.

So it was with some dismay that St. Paul teacher Mark Westpfahl stood in Ronald Reagan Washington National Airport last week and watched a planeload of his students take to the skies without him.

American Airlines had overbooked the flight home to Minneapolis-St. Paul International Airport.

American Airlines may not have understood the first rule of field trips.

“Chaperone Westpfahl?” An apologetic gate agent approached Friday night, as Westpfahl and a fellow teacher were preparing their 11- through 14-year-old charges for the trip home.

Westpfahl, an American studies teacher at St. Paul’s Capitol Hill Gifted And Talented Magnet School, has led a lot of class trips, but this one had been special. The cherry trees were blooming on the National Mall, his students had gotten a special behind-the-scenes tour of the Smithsonian National Museum of Natural History and its vast storerooms of exotic bugs and dinosaur bones. There had been very few blisters.

If you scroll through his Twitter account, @MarkJWestpfahl, you’ll find post after post about the trip. Smiling students, moonlit monuments, the original plans for the Normandy invasion they were allowed to touch, the flowers one student left at the Pentagon’s Sept. 11, 2001, memorial.

Until ...

“I regret to inform you that your name has been randomly pulled to be taken off the flight, because we’re overbooked,” Westpfahl remembered the airline’s representative telling him. “And I’m sitting there with a smile, because I’m trying to figure out, ‘Are they having a little bit of fun with me? Or are they not?’ ”

Westpfahl and his colleague protested. Not only was a 1-to-16 student-to-chaperone ratio less than ideal, Westpfahl was carrying prescriptions for several students who might have needed them during the flight.

“I’m sorry,” Westpfahl remembers the agent telling him. “There’s nothing else we can do.”

The attendants put out a general call for volunteers willing to take a later flight, but didn’t mention that the alternative was splitting a teacher from a group of children in his care.

Nobody volunteered.

“Update: It’s 11:00 p.m. & my students are probably flying over part of West Virginia or Pennsylvania right now … but I’m still sitting here in Reagan National [Airport] because I got bumped from an overbooked @AmericanAir flight,” he tweeted late on the night of April 5. “I’m disappointed & bummed I’m not w/my #CHCougars.”

If you ask the airline, they’ll tell you Westpfahl must have volunteered his way off the flight. That’s what it says in their computer and he received a voucher reserved for people who give up their seats voluntarily. People involuntarily kicked off the flights they paid for are compensated at a different scale.

“According to our records, he volunteered,” the airline said in a statement Thursday. “And he received compensation as a volunteer in addition to American paying for his hotel accommodation. We always seek volunteers before denying anyone boarding.”

It’s a classic “he-said, vast faceless corporation-said” situation.

Either Westpfahl — one of this year’s nominees for Minnesota Teacher of the Year — ditched his students in exchange for a voucher, 2 ½ hours of sleep at an airport motel and a morning redeye back to Minnesota.

Or American is separating adults from children willy-nilly at the boarding gate.

Or maybe, just maybe, there was a mix-up. Maybe somebody punched the wrong button on the computer.

Maybe American Airlines owes the Capitol Hill teachers and students an apology and friendlier skies the next time they fly.

Airline spokesman Ross Feinstein promised to talk to Westpfahl.

“We’re going to reach out to him,” he said. And he followed through. As of Thursday evening, Westpfahl and the airline were playing phone tag.

“This is not the norm,” Feinstein said. “We do not separate families and children.”