When simple things like buying a TV and video player weren't financially feasible anymore, Manfred Timpe turned to the advertising world to bail him out.

The principal of Frankfurt's small Falkschule recently began renting out ad space for €90 ($105) a month to mobile phone and comic book companies, giving them access to his lucrative student body. Teachers and the state school authorities swiftly criticized Timpe's move, but loopholes in the state law have so far kept him in the clear.

"We asked ourselves if this was possible. Is it correct from an educational point of view," said Timpe, who estimated his annual budget at only €13,000, in a Deutsche Welle interview. The money has to be stetched to cover everything from chalk to new computers. "Considering the increasing shortage of money available to schools, it's a welcome help."

Commercial advertising in schools has long been part of daily life in American high schools, where posters advertising candy and chips cover hallways, and school cafeterias sign lucrative contracts with fast-food chains. German schools have been slower to follow.

Three states ban advertising outright, but amid steadily shrinking school budgets most allow their schools to rent out ad space as long as it helps them to buy needed materials.

"There has been advertising in schools for 10 or 20 years without anybody realizing it," said Tino Leutner, head of the ad firm SCHOOL, which does a brisk business in school advertising. "So it's already quite common place …What we need now are clearer guidelines for school legislation."

Lucrative market of 13 million

With an estimated market of 13 million schoolchildren, it's no wonder firms like SCHOOL want existing legislation to be loosened. Recent studies have shown that the buying power of German kids continues to rise. Most teens receive an average monthly allowance of €80 and spend liberally on clothes and mobile phones, according to a recent study by publishers Axel Springer and Bauer Verlag.

That's exactly why teenagers shouldn't receive more encouragement at school, say some.

"There's enough advertising already," says Susanne Levin, a teacher at the Falkschule. "Wherever they go, children are encouraged to spend money on things they don't need, and it doesn't need to happen at school too."

State school authorities agree.

"Fortunately, schools are still a place that can offer an escape from reality, at least in some areas," said Hans-Rolf Eifer, from the Hesse School Authority. "Schools can make students aware of negative developments, which I think shouldn't be taking place everywhere in the first place."