Osbourn Park High students became teachers last week as more than 600 elementary students visited the school for a science-themed carnival.

Led by high school student guides, the younger children moved through outdoor booths devoted to constellations, whales, dolphins, insects and even an eight-foot-tall volcano that emitted puffs of white smoke. Six elementary schools that feed into Osbourn Park participated in the fair: Bennett, Coles, Sudley, Penn, West Gate and Yorkshire.

By the end, the elementary students were fountains of science trivia.

"I learned that insects have two stomachs," said Sarah Marmelstein, a fourth-grader from Penn Elementary. "And I learned that the pressure and heat make volcanoes erupt."

The 10-year-old said she liked visiting Osbourn Park, too. "It's cool, because I like learning what they do and what they have to learn to do all this stuff," she said. "And I like learning lots of facts."

The specialty program at Osbourn Park, once known as the Center for Environmental and Biological Sciences, is changing focus this fall to biotechnology. For five years, students in the specialty program have ended the school year with an event for Sudley Elementary students, because that school has a math and science focus.

Jane Jones, an Osbourn Park biotech humanities teacher, said teachers brainstormed this year to figure out ways to expand their reach. "All the teachers have been charged with deciding, 'How do you pass on the learning?' " she said.

Thus, the expanded event was born. Freshmen and sophomores came up with environmental themes in October, then wrote scripts and built elaborate props during the year to bring their ideas to life. Juniors and seniors served as escorts. In all, about 200 students participated. They were graded not only on their projects but also on how well they were able to share their knowledge with a younger crowd.

Sometimes project ideas came from unexpected sources.

"We came up with the idea when we were walking through Target and we found a bunch of whale stuff and thought it was cute," said freshman Christine Graham, 14. Her group decided to create a booth where students could learn about captive whales and wild whales.

"It's actually turned out really good," Christine said. "I have a young sister at home, so it's really easy to be with them."

Freshmen Michael Dennis and Zak White, both 14, came up with the volcano idea. They worked on it for more than two months, without any plans or blueprints. "We kind of built it as we went along," Zak said.

Their first plan was to build a volcano 20 feet high, but they scaled down their ambitions. The elementary students didn't seem to mind as they crawled inside the structure to check out the smoke machine.

"They seem to like it," Michael said.

In fact, they seemed not to be able to stay away from it. Every student group seemed to stop by the volcano. "There's so many kids. They're like cicadas," Zak said.

The elementary students also got to observe another interesting creature: teenagers in their natural habitat.

"My brother goes here, so I've been here lots of times. But I like coming here a lot," said 10-year-old Samantha San Pietro, a fourth-grader from Penn.

Two Bennett second-graders saw one booth demonstration dissolve into splashy fun.

"They have all kinds of fights, throwing water balloons," said Alexzander Ballard, 7.

"They like to do that stuff," said 8-year-old Rebecca Beverly, giggling.

Jones said the event turned out so well that teachers and students want to do it again next year. The high school students noted that the younger kids are already science savvy, so next year they might write more advanced scripts. They also want to put booths closer together, so the event feels more like a carnival. And next year they might invite even more students from elementary schools to join in.

"We realize the elementary school students benefited so much from it," Jones said.

Sophomore Britt Lyddane, 16, shows a live cicada to Penn Elementary student Jose Martinez, 10, at the Osbourn Park science carnival. Bennett Elementary student Alex Starnes, 8, checks out a trail bike at the parks exhibit. Osbourn Park's lizard booth was one of many educational exhibits focusing on scientific themes. There was even a smoke-emitting volcano.