SARASOTA - Too busy to notice the sweat beads bubbling on their foreheads, 30 students from Harllee Middle School hammered nails and poured concrete into giant molds Tuesday.

For five hours in the sun, they hurried back and forth between quick water breaks to pull apart the molds and reveal their new creations: environmentally-friendly reef balls.

The students have been learning the effects of human impact on biological diversity as part of sixth-grade science teacher Rick Smith's lesson plan.

"It's been the best learning opportunity I've ever seen," Smith said. "The kids absolutely love it, and they have a chance to make a positive impact on the environment."

This was their fourth and final trip to Reef Innovations in Sarasota, where they have been constructing nearly 90 reef balls of varying size since March.

"It's fun because we get to help the environment," said sixth-grader Pharnette Richemond. "Since the water is polluted right now, the fish will have a place to live."

Mimicking natural reef systems, the balls create habitats for fish and other marine and freshwater species. The durable concrete should last up to 500 years in the water, Smith said. In July, they will be deployed in Sarasota Bay.

Two of the balls will be marked with bronze medallions and monitored with underwater cameras. In six months, Smith estimated, the balls will be completely covered with marine growth, and the students will witness that transformation on video tape.

"It feels really good to be able to do this," said sixth-grader Travis Hammond. "I like the hands-on experience the most."

Seventh-grader Becca Cook, who wants to be a marine biologist when she grows up, concurred. "I like playing with the concrete. It gets all over you."

But the project is not only about science, Smith said, it is about life lessons.

Harllee Middle School, a magnet school for engineering technology, is located in one of the highest crime areas in Bradenton and the students need a positive outlet, Smith said.

When studying the benefits of reef balls, students learn that grouper and pinfish, who usually have a predator/prey relationship, often live together.

"It teaches them about co-habitation," Smith said. "If they can get along, then we can get along."

In addition to the regular curriculum, many students participate in Science is Cool After School, a component of the Boys and Girls Club that provides students with an extra two hours of reef ball instruction every week after classes.

Local organizations are catching on too. The Under the Dock Program for the Manatee County Environmental Protection Agency recently provided the school with a $43,000 grant to be their main producer of reef balls, Smith said. Next year, with these funds, the school hopes to build a facility on campus with molds and materials.

The students have been involved in every aspect of the project from composing grant proposals to building the reef balls, he said.

Students wrote to the Sarasota Bay Estuary Program and received $3,000 from the organization. Harllee's School Advisory Committee awarded the students another $1,000.

"It doesn't cost the school board a dime," said Smith, which also pleased Harllee Middle School Principal Guy Davis.

"We're really impressed with the success of this," Davis said. "It's great for the environment, and the county and school board are bonding."

Curriculum Specialist Shelbi Weaver was amazed at the students' level of motivation. As soon as the students get off the bus, she said, they run to their molds and start working.

"They're giving back to the community, which is what we try to nurture in them," she said. "This is something they'll be able to tell their great-grandchildren about."

For more information on reef balls, go to http://reefball.org/.