To make a switch to illuminate the lighthouse when a ball dropped in, Hannon cut an extension cord with wire cutters at home, he explained, and plugged it in.
"Then I touched it," he said. "It really hurt."
An aspiring civil engineer, Hannon might some day build dams or bridges. And Growney might discover a better way to test medicines, or invent a synthetic fabric. He wants to be a chemical engineer.
For now, however, they are still two of 20 Shawnee upperclassmen learning what it takes to design and build a construction project on deadline.
For three years, technology education teacher Stefani Kirk has required her students to make mini-golf courses.
"They're real-world projects" that let students "see their brainstorms start as pencil sketches," she said, "and evolve into something people actually use."
At 5:30 p.m., the doors were to open on "family fun night," when members of the public pay $1 apiece to play the course. But many of the students were still tweaking their projects as deadline approached.
In Kirk's classroom, Walter Tebbs was experimenting with an electric motor.
"It was supposed to turn that bicycle wheel," he said, "but it goes way too fast."
His would-be Ferris wheel, ringed with empty Chinese-food cartons, was supposed to occlude golfers' view of the hole, he said. But it was spinning way too fast, and the spokes were flying off. "We decided it was too dangerous."
With little more than two hours before the Brownies were to arrive, Tebbs wore an air of desperation. He began experimenting with a foam propeller he hoped would lift struck balls as they passed over a two-foot jump in the floor of his project, but it wasn't working.
"I'd rather have a boring hole than one that does not work," said Tebbs, but he had not given up; he was studying ways to make a string of plastic pennants dance over his course.
As the clock ticked closer to starting time, more students arrived to finish their projects, and there was urgency in the air.
"I need a heat gun!" Max Goldstein announced at the door of Kirk's classroom at 4:19 p.m. Nine minutes later, he was back, wanting to know "where can I fill up a bucket of water" for his water hazard.
At the atrium, Lauren Coker and Lacey Michaels were dumping sand from Wildwood into the Mickey Mouse-shaped sand traps of their Disney-themed course hole.
Their giggles faded, however, as they noted how their plywood floor wobbled under a player's weight. And the PVC tube that was supposed to steer a ball to a hole-in-one wasn't angled sharply enough.
"I wish I had more powerful speakers," lamented Jack Cohen, whose graveyard-themed project, with a Styrofoam headstone, featured his partner's recorded voice intoning, "rest in peeeeeeace" when the ball landed.
Austin Marias and Jackson Schrieder, meanwhile, were adjusting the control that regulated a rotating bar in the path of their project, obliging golfers to time their ball-strikes.
At 5 p.m., there was still no sign of Brett Piech, Joe Messler, or their project.
"They skipped school today to finish," Hannon said.
Then, at 5:19, two pickup trucks bearing their project arrived. In four parts, the size of two ping-pong tables, it needed eight boys to carry in.
"Joe, it's not done," said one.
"It's done, it's just not set up," said Messler. "Hey, wait: when does this thing start?"
"You've got seven minutes," Hannon replied.
Piech and Messler were still setting up in a hall when the doors opened, and the first of dozens of Brownies and other young children began pouring in.
Wielding plastic-headed putters and colored golf balls, they headed for the first hole, where Marias and Schrieder's rotating bar waited to vex them.
First up was Elizabeth Adler, 8, of Medford, wearing the brown sash of Troop 21266. She hit her ball, which hit the twirling bar, and bounced back at her.
Puzzled, she hit it again and again, trying to step out of the way of the bar as she took aim. Finally, she picked up her ball and placed it farther down the course. After about 17 attempts to hit it into the hole, which was on a steep slope, she pushed it in with her hand and moved on.
And so it went.
The carpet on the graveyard-themed hole proved thick and slow. The spaces on either side of Hannon's lighthouse were too narrow to let a ball through. And Growney and his partner, McKenna Paschell, spent much of the evening reaching into their gold-painted toilet tank to fetch unplayable balls.
None of the young players seemed to mind the flaws, however - or even to keep score. If a hole proved too tough, they slid the ball along hockey-style, or dropped it in with their hands.
Grown-ups, too, seemed unfazed by the flaws in these youthful, first-time efforts.
"What a neat thing for the older kids," said Kristine Adler, Elizabeth's mother. "To build it and see it come to life and be enjoyed - it's a whole new part of a science experiment."
By 6 p.m., Marias and Schrieder had turned off the rotating bar, and Tebbs, who had abandoned his electric motor, was philosophical.
"That's how it goes most days," said the Medford Lakes senior, who will enter the University of Tennessee as an engineering major in the fall.
"On paper, it's perfect," he said with a shrug.
"In practice, that's where you learn a lesson."