Even the butterflies sensed something was up.
Maybe it was the fidgetier-than-usual little bodies in the classroom seats around them.
Maybe it was the hint of chill in the air, calling forth the urgings of ancestors past.
Flitting about their mesh enclosures in orange-and-black-winged flight, the monarchs were on the move. Ready to go. Even a dish of Juicy Juice, their favorite, the green kind, wasn't getting many takers.
"I'm soooo excited, I can't stop smiling," said Algerita Phillips, a fifth grader at the Thomas E. Bowe School in Glassboro.
In just hours, the students would release the monarchs in the school's butterfly garden, allowing them to join their species' epic migration to Mexico.
The children had already begun their own far-ranging journey of knowledge, "a jump start" - in the words of their teacher Holly Conaway - on the school year, inspired by their winged comrades.
They've learned about the monarch life cycle, written about butterflies, and done a butterfly project in art. Over the months, they will correspond with Mexican children, study Spanish language and culture, and learn more about conservation and ecology.
Butterflies will even flutter through math problems.
"I try to include monarchs in all subjects," Conaway said.
Said Dylan Acri, 10: "When I first came to this class and saw all the caterpillars, I thought, 'Oh, my God, this teacher is crazy,' but now I feel it's the coolest class."
Conaway is among about 4,000 educators in 15 states and four Canadian provinces who have received training since 2001 from the Monarch Teacher Network, a part of the nonprofit Educational Information and Resource Center in Gloucester County.
Enriching the education experience is the network's goal. So is instilling respect for the natural world and its creatures.
Monarchs haven't had an easy time, with deforestation in Mexico and loss of habitat to development in the United States topped by severe storms south of the border.
"This past winter was the lowest population that survived the Mexican winter in 20 years," network director Erik Mollenhauer said.
Their numbers have since grown, but concerns about their long-term prospects remain.
On the day of the Glassboro monarchs' release, some of the children admitted to mixed emotions about saying goodbye. After all, they and the monarchs go way back - to caterpillarhood, or even eggs. Granted, that was only weeks earlier, but weeks can seem like a long time when you're 10 and even longer for a butterfly.
Conaway sought to soothe.
"One of the neat things is this isn't the end," the teacher told them. Around Halloween, when the monarchs reach Mexico, her class will make sugar skulls and talk about Mexico's Dia de los Muertos, Day of the Dead, and the notion that the arriving butterflies carry the souls of the dearly departed.
Then in March, she continued, the students will follow the butterflies' return on the website Journeynorth.org.
Conaway's passion transcends the academic.
She keeps a butterfly garden at her home; driving, she brakes for milkweed, the plant on which monarchs lay their eggs and the caterpillars feed; she hand-feeds the butterflies born in her class to make sure they eat; and she wears monarch earrings and a necklace shaped like a green monarch chrysalis, right down to the golden flecks.
It wasn't always so.
Despite growing up in downtown Glassboro, Conaway, the wife of a pastor and mother of two college-age kids, had a thing for birds - until she saw rats running up her bird feeder.
Seeing a brochure for the Monarch Teacher Network, she thought, "How cool."
Since taking the course seven years ago, she has made monarchs an ever larger part of her curriculum.
Others at Bowe are also smitten. Jennifer Versak-Kennedy raises monarchs in her classroom to inspire her art classes. Spanish teacher Marilyn Appel has her students paint paper butterflies and mails them to youngsters in Mexico, hoping they'll write back.
And Cheryl Tartaglione, the special-education teacher in Conaway's classroom, calls herself "a milkweed freak."
"I've gone on private property to get it. My husband said, 'You're going to be arrested.' "
Truth is, monarchs are fascinating.
While most live only weeks, intent on reproducing, monarchs that emerge from their chrysalises in mid- or late August are born to greater things.
"A genetic switch slips, and instead of being interested in sex, they're just interested in travel," said the monarch network's Mollenhauer. "They just say no, and instead of living three to five weeks, they live eight months."
These monarchs fly south 2,000 or more miles (by early October, they had reached Texas) to quietly pass the winter in the oyamel trees of Mexico's heartland.
In late February, they are again on the move, and by late March, they're back in Texas and Oklahoma, laying their eggs in milkweed, said Chip Taylor, director of the University of Kansas' Monarch Watch project. When those butterflies emerge, they fly north to repeat the life cycle.
Milkweed is noxious to many birds, so it protects the eggs and, later, the caterpillars, Conaway said. The butterflies' bold colors warn predators that they've acquired their former diet's properties.
But Conaway's students already know that - and more.
"I thought it was cool that they could taste with their feet," said Jacob Uscilowski, 10.
Kevin Diaz, 10, was amazed to learn that butterflies have scales. And he said he had told his mother stuff about her native Mexico that she hadn't known.
"I want to go to a Day of the Dead party," said Brittany Miller, 11, who also wants to visit Mexico. "It sounds like fun."
Finally, the big moment for the children - and the 26 butterflies - arrived outside in the butterfly garden.
Holly Felker, 10, toted a camera to snap the monarchs, which she had named and could tell apart. Cheryl is the shy one, she said, and "Brainiac is really smart."
"Ready?" Conaway called out.
"Set?" asked art teacher Versak-Kennedy. And then, "Go to Mexico!"
"Ooooo! Ahhhh!" was the chorus as wings fluttered skyward. A few reluctant monarchs had to be coaxed. Little hands were eager to assist.
Conaway, a bit wistful, mused that some of the monarchs they will raise next year may be offspring of the butterflies they just released.
"It's going to be a beautiful weekend," she said. "It'll give them a fighting chance. Maybe they'll catch a tailwind to Mexico."