To help warm up students who are cool to the subject of rocks, teacher Garry vom Lehn puts it in the context of his own climb up Mount Kilimanjaro.
The Mount Airy Middle School science teacher shows his class a slide of him and his climbing party on the spot where Kilimanjaro spewed molten lava to form igneous rock some 700,000 years earlier.
An avid hiker since he was a teen-ager, Mr. vom Lehn graduated to mountain climbing in 1984, starting with the mountains in Scotland, where he spent part of his childhood. A year ago, he climbed Kilimanjaro, one of the tallest mountains in the world at 19,340 feet.
This summer, he went climbing in the Tien Shan mountains in Central Asia.
Friday was the first anniversary of the day Mr. vom Lehn stood at the summit of Kilimanjaro, in the East African country of Tanzania. He used the occasion to preview a unit on volcanoes, which the eighth-graders will study after they complete a unit on glaciers.
"This is a giant volcano, and what you're looking at is a view across the crater. I'm standing at the rim of the crater," Mr. vom Lehn told the students.
Student Christy Arnone raised her hand to ask how Mr. vom Lehn would know if the volcano were about to erupt. He tells her scientists can tell when a volcano is dormant, but that the first sign would be a smell of sulfur.
Having a teacher who's been to the place shown in the slide -- and in many cases took the pictures himself -- makes the material more credible, she said.
"We're hearing it from the person who was there, so we can sort of believe him," she said.
And while anyone can tell a class that mountain climbing is physically taxing, Mr. vom Lehn can demonstrate the pace and breathing of climbing at levels of 17,000 feet and higher.
He takes two slow steps, stops and inhales slowly, laboriously. He does it again, then takes two more slow steps.
"That's what life is like at 17,000 feet. The pace is very slow," he said.
During part of the five-day climb and two-day descent, the climbing party went to bed at 6:30 p.m. and awoke at 12:30 a.m., because that was the best time to climb and because sleeping and eating patterns change drastically.
"At high altitudes, you don't eat well, and you don't sleep well," he said. "Your body has to adjust."
Mount Kenya loomed in the background of the slide showing Mr. vom Lehn atop Kilimanjaro. The mountains are 200 miles apart.
In case those numbers didn't mean much to the students, Mr. vom Lehn put them in a more local context.
"That's like the distance from New York to Washington, D.C.," he told them. And it would be like standing atop the Washington Monument and seeing the Empire State Building, if those two edifices were as tall as the mountains.
Mr. vom Lehn had to get approval from his principal and the personnel office to take time off during the school year for his climb, even though he took mostly unpaid days. But his principal never questioned that Mr. vom Lehn's trip would be worthwhile.
"He's talking about first-hand experiences. Just that ability builds excitement in kids," said Mount Airy Middle School Principal Larry Barnes. "And I envy him."
But Mr. vom Lehn, who has been teaching 19 years at Mount Airy Middle School, said, "Any strategy that you bring in, as good as it might be, it will reach some kids and not others."
What works best, he said, is to put students at the center of a demonstration. This fall, he has plans to do just that, but won't divulge the details.
The plan involves mountain-climbing gear and equipment, though, and the students will be able to touch it, not just watch a slide.
While Mr. vom Lehn gets excited about his adventures, the boredom of some of the students deflates his enthusiasm.
"Because of that, I don't say, 'Now, for the next two days, we're going to talk about all my travels,' " he said.
Throughout the year, he often takes students, in groups of 10 or 20, for Saturday hikes on trails in Maryland. A few of the trips have a science theme and some built-in experiments and exercises, but most are recreational.
For the immediate future, Mr. vom Lehn plans to stay close to his home in Frederick. He and his wife, Nancy, had their first child 12 weeks ago.