Then it got personal.

The classroom samples taken by the 20 Excel High School students came back from the lab showing high levels of lead - a dangerous metal known to cause a wide range of neurological and developmental problems, with small children most at risk.

In announcing the results Monday at the school, the students and their advisers said one of the tests showed levels at least five times above the federal Environmental Protection Agency standards for an indoor windowsill.

Those levels could be up to 54 times higher than EPA standards for indoor samples, said Denny Larson of the Global Community Monitor, a San Francisco-based nonprofit group that promotes community involvement in environmental issues. The group sponsored the testing and helped train the students.

"It was devastating when we got our test results back," said 15-year-old Terranisha Nathaniel.

The students collected two samples in November, following scientific procedure as they prepared the plate that would sit undisturbed on a classroom shelf for a week with the window sometimes opened during the day.

The students then swiped the fallout and sent the samples to a EPA-accredited lab.

The method produced preliminary results showing the presence of lead. But it isn't considered reliable for measuring quantities of the dangerous metal in the air or surface areas at the school, said Karen Schkolnick, spokeswoman for the Bay Area Air Quality Management District.

It also doesn't provide any information as to where the lead came from, she added.

While lead is rarely used in industrial processes now, the metal remains in soil, cars and homes. Urban areas are especially prone, given traffic and current or past industry.

Other than accumulated lead in buildings and soil, the largest current source of the metal is from piston-engine aircraft - small propeller planes, Schkolnick said.

Such local testing, sometimes called community monitoring, is becoming more common, said Shana Lazerow, staff attorney for Communities for a Better Environment, a California environmental activist group.

"It's very, very important from a community empowerment perspective," she said.

Students at Excel - formerly McClymonds High School - said they feel empowered and have already asked Schkolnick's agency to give them a more sophisticated air-quality monitor they could use to do more extensive testing. That request is under review, the spokeswoman said.

The teens want to do the testing themselves, said their legal studies teacher, Ina Bendich.

"Students want to be involved in that testing," she said. "They want to be a part of it."

The math and the science are a means to an end now for the students, who are enthusiastic and becoming more involved and invested in the health and safety of their community, she added.

"This is something people don't think about in everyday life," Terranisha said. "This pollution falls on their homes and gets in their kids' system and their own too, and it shortens lives. People should know this is very serious."

E-mail Jill Tucker at jtucker@sfchronicle.com.