Tom Farber gives a lot of tests. He's a calculus teacher, after all.

So when administrators at Rancho Bernardo, his suburban San Diego high school, announced the district was cutting spending on supplies by nearly a third, Farber had a problem. At 3 cents a page, his tests would cost more than $500 a year. His copying budget: $316. But he wanted to give students enough practice for the big tests they'll face in the spring, such as the Advanced Placement exam.

"Tough times call for tough actions," he says. So he started selling ads on his test papers: $10 for a quiz, $20 for a chapter test, $30 for a semester final.

San Diego magazine and The San Diego Union-Tribune featured his plan just before Thanksgiving, and Farber came home from a few days out of town to 75 e-mail requests for ads. So far, he has collected $350. His semester final is sold out.

That worries Robert Weissman, managing director of Commercial Alert, a Washington-based nonprofit that fights commercialization in school and elsewhere.

If test-papers-as-billboards catches on, he says, schools in the grip of tough economic times could start relying on them to help the bottom line.

"The advertisers are paying for something, and it's access to kids," he says.

About two-thirds of Farber's ads are inspirational messages underwritten by parents.

Others are ads for local businesses, such as two early ones from a structural engineering firm and one from a dentist who urges students, "Brace Yourself for a Great Semester!"

Principal Paul Robinson says reaction has been "mixed," but he notes, "It's not like, 'This test is brought to you by McDonald's or Nike.' "

To Farber, 47, it's a logical solution: "We're expected to do more with less."

The National Education Association says teachers spend about $430 out of their pockets each year for school supplies. This semester, Christine Van Ruiten, a teacher at E.C. Reems, a charter school in East Oakland, Calif., has spent $2,000. She scours Craigslist for free supplies and posts requests to Donors Choose.org, which matches teachers with donors.

Founded in 2000 by Charles Best, then a Bronx teacher, DonorsChoose has funded about 65,000 projects totaling $26 million.

Best calls it "a more dignified, substantive alternative for teachers than selling candy door-to-door — and certainly than selling ad space on final exams. That's crazy."